From: "H.J. Lu" <hjl.tools@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH 2/2] x86: Add generic CPUID data dumper to ld.so --list-diagnostics
Date: Fri, 9 Feb 2024 11:34:07 -0800 [thread overview]
Message-ID: <CAMe9rOqPoo9bqKv+7uih=hR0NfFb2KRWeo2AY9cJggm_eYgx8Q@mail.gmail.com> (raw)
In-Reply-To: <269f789e34149703b043898603acdaec3a58f3dc.1707505012.git.fweimer@redhat.com>
On Fri, Feb 9, 2024 at 11:09 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> This is surprisingly difficult to implement if the goal is to produce
> reasonably sized output. With the current approaches to output
> compression (suppressing zeros and repeated results between CPUs,
> folding ranges of identical subleaves, dealing with the %ecx
> reflection issue), the output is less than 600 KiB even for systems
> with 256 threads.
> ---
> manual/dynlink.texi | 86 +++-
> .../linux/x86/dl-diagnostics-cpu-kernel.c | 457 ++++++++++++++++++
> 2 files changed, 542 insertions(+), 1 deletion(-)
> create mode 100644 sysdeps/unix/sysv/linux/x86/dl-diagnostics-cpu-kernel.c
>
> diff --git a/manual/dynlink.texi b/manual/dynlink.texi
> index 06a6c15533..1f02124722 100644
> --- a/manual/dynlink.texi
> +++ b/manual/dynlink.texi
> @@ -228,7 +228,91 @@ reported by the @code{uname} function. @xref{Platform Type}.
> @item x86.cpu_features.@dots{}
> These items are specific to the i386 and x86-64 architectures. They
> reflect supported CPU features and information on cache geometry, mostly
> -collected using the @code{CPUID} instruction.
> +collected using the CPUID instruction.
> +
> +@item x86.processor[@var{index}].@dots{}
> +These are additional items for the i386 and x86-64 architectures, as
> +described below. They mostly contain raw data from the CPUID
> +instruction. The probes are performed for each active CPU for the
> +@code{ld.so} process, and data for different probed CPUs receives a
> +uniqe @var{index} value. Some CPUID data is expected to differ from CPU
> +core to CPU core. In some cases, CPUs are not correctly initialized and
> +indicate the presence of different feature sets.
> +
> +@item x86.processor[@var{index}].requested=@var{kernel-cpu}
> +The kernel is told to run the subsequent probing on the CPU numbered
> +@var{kernel-cpu}. The values @var{kernel-cpu} and @var{index} can be
> +distinct if there are gaps in the process CPU affinity mask. This line
> +is not included if CPU affinity mask information is not available.
> +
> +@item x86.processor[@var{index}].observed=@var{kernel-cpu}
> +This line reports the kernel CPU number @var{kernel-cpu} on which the
> +probing code initially ran. This line is only printed if the requested
> +and observed kernel CPU numbers differ. This can happen if the kernel
> +fails to act on a request to change the process CPU affinity mask.
> +
> +@item x86.processor[@var{index}].observed_node=@var{node}
> +This reports the observed NUMA node number, as reported by the
> +@code{getcpu} system call. It is missing if the @code{getcpu} system
> +call failed.
> +
> +@item x86.processor[@var{index}].cpuid_leaves=@var{count}
> +This line indicates that @var{count} distinct CPUID leaves were
> +encountered. (This reflects internal @code{ld.so} storage space, it
> +does not directly correspond to @code{CPUID} enumeration ranges.)
> +
> +@item x86.processor[@var{index}].ecx_limit=@var{value}
> +The CPUID data extraction code uses a brute-force approach to enumerate
> +subleaves (see the @samp{.subleaf_eax} lines below). The last
> +@code{%rcx} value used in a CPUID query on this probed CPU was
> +@var{value}.
> +
> +@item x86.processor[@var{index}].cpuid.eax[@var{query_eax}].eax=@var{eax}
> +@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].ebx=@var{ebx}
> +@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].ecx=@var{ecx}
> +@itemx x86.processor[@var{index}].cpuid.eax[@var{query_eax}].edx=@var{edx}
> +These lines report the register contents after executing the CPUID
> +instruction with @samp{%rax == @var{query_eax}} and @samp{%rcx == 0} (a
> +@dfn{leaf}). For the first probed CPU (with a zero @var{index}), only
> +leaves with non-zero register contents are reported. For subsequent
> +CPUs, only leaves whose register contents differs from the previously
> +probed CPUs (with @var{index} one less) are reported.
> +
> +Basic and extended leaves are reported using the same syntax. This
> +means there is a large jump in @var{query_eax} for the first reported
> +extended leaf.
> +
> +@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].eax=@var{eax}
> +@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ebx=@var{ebx}
> +@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ecx=@var{ecx}
> +@itemx x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].edx=@var{edx}
> +This is similar to the leaves above, but for a @dfn{subleaf}. For
> +subleaves, the CPUID instruction is executed with @samp{%rax ==
> +@var{query_eax}} and @samp{%rcx == @var{query_ecx}}, so the result
> +depends on both register values. The same rules about filtering zero
> +and identical results apply.
> +
> +@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].until_ecx=@var{ecx_limit}
> +Some CPUID results are the same regardless the @var{query_ecx} value.
> +If this situation is detected, a line with the @samp{.until_ecx}
> +selector ins included, and this indicates that the CPUID register
> +contents is the same for @code{%rcx} values between @var{query_ecx}
> +and @var{ecx_limit} (inclusive).
> +
> +@item x86.processor[@var{index}].cpuid.subleaf_eax[@var{query_eax}].ecx[@var{query_ecx}].ecx_query_mask=0xff
> +This line indicates that in an @samp{.until_ecx} range, the CPUID
> +instruction preserved the lowested 8 bits of the input @code{%rcx} in
> +the output @code{%rcx} registers. Otherwise, the subleaves in the range
> +have identical values. This special treatment is necessary to report
> +compact range information in case such copying occurs (because the
> +subleaves would otherwise be all different).
> +
> +@item x86.processor[@var{index}].xgetbv.ecx[@var{query_ecx}]=@var{result}
> +This line shows the 64-bit @var{result} value in the @code{%rdx:%rax}
> +register pair after executing the XGETBV instruction with @code{%rcx}
> +set to @var{query_ecx}. Zero values and values matching the previously
> +probed CPU are omitted. Nothing is printed if the system does not
> +support the XGETBV instruction.
> @end table
>
> @node Dynamic Linker Introspection
> diff --git a/sysdeps/unix/sysv/linux/x86/dl-diagnostics-cpu-kernel.c b/sysdeps/unix/sysv/linux/x86/dl-diagnostics-cpu-kernel.c
> new file mode 100644
> index 0000000000..f84331b33b
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86/dl-diagnostics-cpu-kernel.c
> @@ -0,0 +1,457 @@
> +/* Print CPU/kernel diagnostics data in ld.so. Version for x86.
> + Copyright (C) 2023 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <dl-diagnostics.h>
> +
> +#include <array_length.h>
> +#include <cpu-features.h>
> +#include <cpuid.h>
> +#include <ldsodefs.h>
> +#include <stdbool.h>
> +#include <string.h>
> +#include <sysdep.h>
> +
> +/* Register arguments to CPUID. Multiple ECX subleaf values yielding
> + the same result are combined, to shorten the output. Both
> + identical matches (EAX to EDX are the same) and matches where EAX,
> + EBX, EDX, and ECX are equal except in the lower byte, which must
> + match the query ECX value. The latter is needed to compress ranges
> + on CPUs which preserve the lowest byte in ECX if an unknown leaf is
> + queried. */
> +struct cpuid_query
> +{
> + unsigned int eax;
> + unsigned ecx_first;
> + unsigned ecx_last;
> + bool ecx_preserves_query_byte;
> +};
> +
> +/* Single integer value that can be used for sorting/ordering
> + comparisons. Uses Q->eax and Q->ecx_first only because ecx_last is
> + always greater than the previous ecx_first value and less than the
> + subsequent one. */
> +static inline unsigned long long int
> +cpuid_query_combined (struct cpuid_query *q)
> +{
> + /* ecx can be -1 (that is, ~0U). If this happens, this the only ecx
> + value for this eax value, so the ordering does not matter. */
> + return ((unsigned long long int) q->eax << 32) | (unsigned int) q->ecx_first;
> +};
> +
> +/* Used for differential reporting of zero/non-zero values. */
> +static const struct cpuid_registers cpuid_registers_zero;
> +
> +/* Register arguments to CPUID paired with the results that came back. */
> +struct cpuid_query_result
> +{
> + struct cpuid_query q;
> + struct cpuid_registers r;
> +};
> +
> +/* During a first enumeration pass, we try to collect data for
> + cpuid_initial_subleaf_limit subleaves per leaf/EAX value. If we run
> + out of space, we try once more with applying the lower limit. */
> +enum { cpuid_main_leaf_limit = 128 };
> +enum { cpuid_initial_subleaf_limit = 512 };
> +enum { cpuid_subleaf_limit = 32 };
> +
> +/* Offset of the extended leaf area. */
> +enum {cpuid_extended_leaf_offset = 0x80000000 };
> +
> +/* Collected CPUID data. Everything is stored in a statically sized
> + array that is sized so that the second pass will collect some data
> + for all leaves, after the limit is applied. On the second pass,
> + ecx_limit is set to cpuid_subleaf_limit. */
> +struct cpuid_collected_data
> +{
> + unsigned int used;
> + unsigned int ecx_limit;
> + uint64_t xgetbv_ecx_0;
> + struct cpuid_query_result qr[cpuid_main_leaf_limit
> + * 2 * cpuid_subleaf_limit];
> +};
> +
> +/* Fill in the result of a CPUID query. Returns true if there is
> + room, false if nothing could be stored. */
> +static bool
> +_dl_diagnostics_cpuid_store (struct cpuid_collected_data *ccd,
> + unsigned eax, int ecx)
> +{
> + if (ccd->used >= array_length (ccd->qr))
> + return false;
> +
> + /* Tentatively fill in the next value. */
> + __cpuid_count (eax, ecx,
> + ccd->qr[ccd->used].r.eax,
> + ccd->qr[ccd->used].r.ebx,
> + ccd->qr[ccd->used].r.ecx,
> + ccd->qr[ccd->used].r.edx);
>
Please factor out OS independent bits, like CPUID, to
sysdeps/x86.
> + /* If the ECX subleaf is next subleaf after the previous one (for
> + the same leaf), and the values are the same, merge the result
> + with the already-stored one. Do this before skipping zero
> + leaves, which avoids artifiacts for ECX == 256 queries. */
> + if (ccd->used > 0
> + && ccd->qr[ccd->used - 1].q.eax == eax
> + && ccd->qr[ccd->used - 1].q.ecx_last + 1 == ecx)
> + {
> + /* Exact match of the previous result. Ignore the value of
> + ecx_preserves_query_byte if this is a singleton range so far
> + because we can treat ECX as fixed if the same value repeats. */
> + if ((!ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte
> + || (ccd->qr[ccd->used - 1].q.ecx_first
> + == ccd->qr[ccd->used - 1].q.ecx_last))
> + && memcmp (&ccd->qr[ccd->used - 1].r, &ccd->qr[ccd->used].r,
> + sizeof (ccd->qr[ccd->used].r)) == 0)
> + {
> + ccd->qr[ccd->used - 1].q.ecx_last = ecx;
> + /* ECX is now fixed because the same value has been observed
> + twice, even if we had a low-byte match before. */
> + ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte = false;
> + return true;
> + }
> + /* Match except for the low byte in ECX, which must match the
> + incoming ECX value. */
> + if (ccd->qr[ccd->used - 1].q.ecx_preserves_query_byte
> + && (ecx & 0xff) == (ccd->qr[ccd->used].r.ecx & 0xff)
> + && ccd->qr[ccd->used].r.eax == ccd->qr[ccd->used - 1].r.eax
> + && ccd->qr[ccd->used].r.ebx == ccd->qr[ccd->used - 1].r.ebx
> + && ((ccd->qr[ccd->used].r.ecx & 0xffffff00)
> + == (ccd->qr[ccd->used - 1].r.ecx & 0xffffff00))
> + && ccd->qr[ccd->used].r.edx == ccd->qr[ccd->used - 1].r.edx)
> + {
> + ccd->qr[ccd->used - 1].q.ecx_last = ecx;
> + return true;
> + }
> + }
> +
> + /* Do not store zero results. All-zero values usually mean that the
> + subleaf is unsupported. */
> + if (ccd->qr[ccd->used].r.eax == 0
> + && ccd->qr[ccd->used].r.ebx == 0
> + && ccd->qr[ccd->used].r.ecx == 0
> + && ccd->qr[ccd->used].r.edx == 0)
> + return true;
> +
> + /* The result needs to be stored. Fill in the query parameters and
> + consume the storage. */
> + ccd->qr[ccd->used].q.eax = eax;
> + ccd->qr[ccd->used].q.ecx_first = ecx;
> + ccd->qr[ccd->used].q.ecx_last = ecx;
> + ccd->qr[ccd->used].q.ecx_preserves_query_byte
> + = (ecx & 0xff) == (ccd->qr[ccd->used].r.ecx & 0xff);
> + ++ccd->used;
> + return true;
> +}
> +
> +/* Collected CPUID data into *CCD. If LIMIT, apply per-leaf limits to
> + avoid exceeding the pre-allocated space. Return true if all data
> + could be stored, false if the retrying without a limit is
> + requested. */
> +static bool
> +_dl_diagnostics_cpuid_collect_1 (struct cpuid_collected_data *ccd, bool limit)
> +{
> + ccd->used = 0;
> + ccd->ecx_limit
> + = (limit ? cpuid_subleaf_limit : cpuid_initial_subleaf_limit) - 1;
> + _dl_diagnostics_cpuid_store (ccd, 0x00, 0x00);
> + if (ccd->used == 0)
> + /* CPUID reported all 0. Should not happen. */
> + return true;
> + unsigned int maximum_leaf = ccd->qr[0x00].r.eax;
> + if (limit && maximum_leaf >= cpuid_main_leaf_limit)
> + maximum_leaf = cpuid_main_leaf_limit - 1;
> +
> + for (unsigned int eax = 1; eax <= maximum_leaf; ++eax)
> + {
> + for (unsigned int ecx = 0; ecx <= ccd->ecx_limit; ++ecx)
> + if (!_dl_diagnostics_cpuid_store (ccd, eax, ecx))
> + return false;
> + }
> +
> + if (!_dl_diagnostics_cpuid_store (ccd, cpuid_extended_leaf_offset, 0x00))
> + return false;
> + maximum_leaf = ccd->qr[ccd->used - 1].r.eax;
> + if (maximum_leaf < cpuid_extended_leaf_offset)
> + /* No extended CPUID information. */
> + return true;
> + if (limit
> + && maximum_leaf - cpuid_extended_leaf_offset >= cpuid_main_leaf_limit)
> + maximum_leaf = cpuid_extended_leaf_offset + cpuid_main_leaf_limit - 1;
> + for (unsigned int eax = cpuid_extended_leaf_offset + 1;
> + eax <= maximum_leaf; ++eax)
> + {
> + for (unsigned int ecx = 0; ecx <= ccd->ecx_limit; ++ecx)
> + if (!_dl_diagnostics_cpuid_store (ccd, eax, ecx))
> + return false;
> + }
> + return true;
> +}
> +
> +/* Call _dl_diagnostics_cpuid_collect_1 twice if necessary, the
> + second time with the limit applied. */
> +static void
> +_dl_diagnostics_cpuid_collect (struct cpuid_collected_data *ccd)
> +{
> + if (!_dl_diagnostics_cpuid_collect_1 (ccd, false))
> + _dl_diagnostics_cpuid_collect_1 (ccd, true);
> +
> + /* Re-use the result of the official feature probing here. */
> + const struct cpu_features *cpu_features = __get_cpu_features ();
> + if (CPU_FEATURES_CPU_P (cpu_features, OSXSAVE))
> + {
> + unsigned int xcrlow;
> + unsigned int xcrhigh;
> + asm ("xgetbv" : "=a" (xcrlow), "=d" (xcrhigh) : "c" (0));
> + ccd->xgetbv_ecx_0 = ((uint64_t) xcrhigh << 32) + xcrlow;
> + }
> + else
> + ccd->xgetbv_ecx_0 = 0;
> +}
> +
> +/* Print a CPUID register value (passed as REG_VALUE) if it differs
> + from the expected REG_REFERENCE value. PROCESSOR_INDEX is the
> + process sequence number (always starting at zero; not a kernel ID). */
> +static void
> +_dl_diagnostics_cpuid_print_reg (unsigned int processor_index,
> + const struct cpuid_query *q,
> + const char *reg_label, unsigned int reg_value,
> + bool subleaf)
> +{
> + if (subleaf)
> + _dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
> + ".ecx[0x%x].%s=0x%x\n",
> + processor_index, q->eax, q->ecx_first, reg_label, reg_value);
> + else
> + _dl_printf ("x86.processor[0x%x].cpuid.eax[0x%x].%s=0x%x\n",
> + processor_index, q->eax, reg_label, reg_value);
> +}
> +
> +/* Print CPUID result values in *RESULT for the query in
> + CCD->qr[CCD_IDX]. PROCESSOR_INDEX is the process sequence number
> + (always starting at zero; not a kernel ID). */
> +static void
> +_dl_diagnostics_cpuid_print_query (unsigned int processor_index,
> + struct cpuid_collected_data *ccd,
> + unsigned int ccd_idx,
> + const struct cpuid_registers *result)
> +{
> + /* Treat this as a value if subleaves if ecx isn't zero (maybe
> + within the [ecx_fist, ecx_last] range), or if eax matches its
> + neighbors. If the range is [0, ecx_limit], then the subleaves
> + are not distinct (independently of ecx_preserves_query_byte),
> + so do not report them separately. */
> + struct cpuid_query *q = &ccd->qr[ccd_idx].q;
> + bool subleaf = (q->ecx_first > 0
> + || (q->ecx_first != q->ecx_last
> + && !(q->ecx_first == 0 && q->ecx_last == ccd->ecx_limit))
> + || (ccd_idx > 0 && q->eax == ccd->qr[ccd_idx - 1].q.eax)
> + || (ccd_idx + 1 < ccd->used
> + && q->eax == ccd->qr[ccd_idx + 1].q.eax));
> + _dl_diagnostics_cpuid_print_reg (processor_index, q, "eax", result->eax,
> + subleaf);
> + _dl_diagnostics_cpuid_print_reg (processor_index, q, "ebx", result->ebx,
> + subleaf);
> + _dl_diagnostics_cpuid_print_reg (processor_index, q, "ecx", result->ecx,
> + subleaf);
> + _dl_diagnostics_cpuid_print_reg (processor_index, q, "edx", result->edx,
> + subleaf);
> +
> + if (subleaf && q->ecx_first != q->ecx_last)
> + {
> + _dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
> + ".ecx[0x%x].until_ecx=0x%x\n",
> + processor_index, q->eax, q->ecx_first, q->ecx_last);
> + if (q->ecx_preserves_query_byte)
> + _dl_printf ("x86.processor[0x%x].cpuid.subleaf_eax[0x%x]"
> + ".ecx[0x%x].ecx_query_mask=0xff\n",
> + processor_index, q->eax, q->ecx_first);
> + }
> +}
> +
> +/* Perform differential reporting of the data in *CURRENT against
> + *BASE. REQUESTED_CPU is the kernel CPU ID the thread was
> + configured to run on, or -1 if no configuration was possible.
> + PROCESSOR_INDEX is the process sequence number (always starting at
> + zero; not a kernel ID). */
> +static void
> +_dl_diagnostics_cpuid_report (unsigned int processor_index, int requested_cpu,
> + struct cpuid_collected_data *current,
> + struct cpuid_collected_data *base)
> +{
> + if (requested_cpu >= 0)
> + _dl_printf ("x86.processor[0x%x].requested=0x%x\n",
> + processor_index, requested_cpu);
> +
> + /* Despite CPU pinning, the requested CPU number may be different
> + from the one we are running on. Some container hosts behave this
> + way. */
> + {
> + unsigned int cpu_number;
> + unsigned int node_number;
> + if (INTERNAL_SYSCALL_CALL (getcpu, &cpu_number, &node_number) >= 0)
> + {
> + if (cpu_number != requested_cpu)
> + _dl_printf ("x86.processor[0x%x].observed=0x%x\n",
> + processor_index, cpu_number);
> + _dl_printf ("x86.processor[0x%x].observed_node=0x%x\n",
> + processor_index, node_number);
> + }
> + }
> +
> + _dl_printf ("x86.processor[0x%x].cpuid_leaves=0x%x\n",
> + processor_index, current->used);
> + _dl_printf ("x86.processor[0x%x].ecx_limit=0x%x\n",
> + processor_index, current->ecx_limit);
> +
> + unsigned int base_idx = 0;
> + for (unsigned int current_idx = 0; current_idx < current->used;
> + ++current_idx)
> + {
> + /* Report missing data on the current CPU as 0. */
> + unsigned long long int current_query
> + = cpuid_query_combined (¤t->qr[current_idx].q);
> + while (base_idx < base->used
> + && cpuid_query_combined (&base->qr[base_idx].q) < current_query)
> + {
> + _dl_diagnostics_cpuid_print_query (processor_index, base, base_idx,
> + &cpuid_registers_zero);
> + ++base_idx;
> + }
> +
> + if (base_idx < base->used
> + && cpuid_query_combined (&base->qr[base_idx].q) == current_query)
> + {
> + _Static_assert (sizeof (struct cpuid_registers) == 4 * 4,
> + "no padding in struct cpuid_registers");
> + if (current->qr[current_idx].q.ecx_last
> + != base->qr[base_idx].q.ecx_last
> + || memcmp (¤t->qr[current_idx].r,
> + &base->qr[base_idx].r,
> + sizeof (struct cpuid_registers)) != 0)
> + /* The ECX range or the values have changed. Show the
> + new values. */
> + _dl_diagnostics_cpuid_print_query (processor_index,
> + current, current_idx,
> + ¤t->qr[current_idx].r);
> + ++base_idx;
> + }
> + else
> + /* Data is absent in the base reference. Report the new data. */
> + _dl_diagnostics_cpuid_print_query (processor_index,
> + current, current_idx,
> + ¤t->qr[current_idx].r);
> + }
> +
> + if (current->xgetbv_ecx_0 != base->xgetbv_ecx_0)
> + {
> + /* Re-use the 64-bit printing routine. */
> + _dl_printf ("x86.processor[0x%x].", processor_index);
> + _dl_diagnostics_print_labeled_value ("xgetbv.ecx[0x0]",
> + current->xgetbv_ecx_0);
> + }
> +}
> +
> +void
> +_dl_diagnostics_cpu_kernel (void)
> +{
> +#if !HAS_CPUID
> + /* CPUID is not supported, so there is nothing to dump. */
> + if (__get_cpuid_max (0, 0) == 0)
> + return;
> +#endif
> +
> + /* The number of processors reported so far. Note that is a count,
> + not a kernel CPU number. */
> + unsigned int processor_index = 0;
> +
> + /* Two copies of the data are used. Data is written to the index
> + (processor_index & 1). The previous version against which the
> + data dump is reported is at index !(processor_index & 1). */
> + struct cpuid_collected_data ccd[2];
> +
> + /* The initial data is presumed to be all zero. Zero results are
> + not recorded. */
> + ccd[1].used = 0;
> + ccd[1].xgetbv_ecx_0 = 0;
> +
> + /* Run the CPUID probing on a specific CPU. There are expected
> + differences for encoding core IDs and topology information in
> + CPUID output, but some firmware/kernel bugs also may result in
> + asymmetric data across CPUs in some cases.
> +
> + The CPU mask arrays are large enough for 4096 or 8192 CPUs, which
> + should give ample space for future expansion. */
> + unsigned long int mask_reference[1024];
> + int length_reference
> + = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0,
> + sizeof (mask_reference), mask_reference);
> +
> + /* A parallel bit mask that is used below to request running on a
> + specific CPU. */
> + unsigned long int mask_request[array_length (mask_reference)];
> +
> + if (length_reference >= sizeof (long))
> + {
> + /* The kernel is supposed to return a multiple of the word size. */
> + length_reference /= sizeof (long);
> +
> + for (unsigned int i = 0; i < length_reference; ++i)
> + {
> + /* Iterate over the bits in mask_request[i] and process
> + those that are set; j is the bit index, bitmask is the
> + derived mask for the bit at this index. */
> + unsigned int j = 0;
> + for (unsigned long int bitmask = 1; bitmask != 0; bitmask <<= 1, ++j)
> + {
> + mask_request[i] = mask_reference[i] & bitmask;
> + if (mask_request[i])
> + {
> + unsigned int mask_array_length
> + = (i + 1) * sizeof (unsigned long int);
> + if (INTERNAL_SYSCALL_CALL (sched_setaffinity, 0,
> + mask_array_length,
> + mask_request) == 0)
> + {
> + /* This is the CPU ID number used by the
> + kernel. It should match the first result
> + from getcpu. */
> + int requested_cpu = i * ULONG_WIDTH + j;
> + _dl_diagnostics_cpuid_collect
> + (&ccd[processor_index & 1]);
> + _dl_diagnostics_cpuid_report
> + (processor_index, requested_cpu,
> + &ccd[processor_index & 1],
> + &ccd[!(processor_index & 1)]);
> + ++processor_index;
> + }
> + }
> + }
> + /* Reset the mask word, so that the mask has always
> + population count one. */
> + mask_request[i] = 0;
> + }
> + }
> +
> + /* Fallback if we could not deliberately select a CPU. */
> + if (processor_index == 0)
> + {
> + _dl_diagnostics_cpuid_collect (&ccd[0]);
> + _dl_diagnostics_cpuid_report (processor_index, -1, &ccd[0], &ccd[1]);
> + }
> +}
> --
> 2.43.0
>
--
H.J.
next prev parent reply other threads:[~2024-02-09 19:34 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-09 19:08 [PATCH 0/2] Enhanced x86 CPU diagnostics Florian Weimer
2024-02-09 19:08 ` [PATCH 1/2] elf: Wire up _dl_diagnostics_cpu_kernel Florian Weimer
2024-02-09 19:08 ` [PATCH 2/2] x86: Add generic CPUID data dumper to ld.so --list-diagnostics Florian Weimer
2024-02-09 19:34 ` H.J. Lu [this message]
2024-02-10 0:44 ` H.J. Lu
-- strict thread matches above, loose matches on Subject: below --
2023-09-08 20:09 [PATCH 1/2] elf: Wire up _dl_diagnostics_cpu_kernel Florian Weimer
2023-09-08 20:10 ` [PATCH 2/2] x86: Add generic CPUID data dumper to ld.so --list-diagnostics Florian Weimer
2023-09-10 19:56 ` Noah Goldstein
2023-09-11 4:24 ` Florian Weimer
2023-09-11 16:16 ` Noah Goldstein
2023-09-11 16:25 ` Florian Weimer
2023-09-11 16:28 ` Noah Goldstein
2023-09-11 16:31 ` Noah Goldstein
2023-09-11 17:48 ` Florian Weimer
2023-09-11 18:35 ` Noah Goldstein
2023-09-11 16:08 ` Adhemerval Zanella Netto
2023-09-11 16:19 ` Florian Weimer
2023-09-11 16:41 ` Adhemerval Zanella Netto
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAMe9rOqPoo9bqKv+7uih=hR0NfFb2KRWeo2AY9cJggm_eYgx8Q@mail.gmail.com' \
--to=hjl.tools@gmail.com \
--cc=fweimer@redhat.com \
--cc=libc-alpha@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).