public inbox for glibc-cvs@sourceware.org
help / color / mirror / Atom feed
* [glibc/release/2.33/master] x86: Adding an upper bound for Enhanced REP MOVSB.
@ 2022-05-02 21:29 Sunil Pandey
0 siblings, 0 replies; only message in thread
From: Sunil Pandey @ 2022-05-02 21:29 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=374d54d0a07a57525b58cf0ed04be1969c67d20e
commit 374d54d0a07a57525b58cf0ed04be1969c67d20e
Author: Sajan Karumanchi <sajan.karumanchi@amd.com>
Date: Tue Feb 2 12:42:14 2021 +0100
x86: Adding an upper bound for Enhanced REP MOVSB.
In the process of optimizing memcpy for AMD machines, we have found the
vector move operations are outperforming enhanced REP MOVSB for data
transfers above the L2 cache size on Zen3 architectures.
To handle this use case, we are adding an upper bound parameter on
enhanced REP MOVSB:'__x86_rep_movsb_stop_threshold'.
As per large-bench results, we are configuring this parameter to the
L2 cache size for AMD machines and applicable from Zen3 architecture
supporting the ERMS feature.
For architectures other than AMD, it is the computed value of
non-temporal threshold parameter.
Reviewed-by: Premachandra Mallappa <premachandra.mallappa@amd.com>
(cherry picked from commit 6e02b3e9327b7dbb063958d2b124b64fcb4bbe3f)
Diff:
---
sysdeps/x86/cacheinfo.h | 4 ++++
sysdeps/x86/dl-cacheinfo.h | 15 ++++++++++++++-
sysdeps/x86/include/cpu-features.h | 2 ++
sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S | 7 +++++--
4 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/sysdeps/x86/cacheinfo.h b/sysdeps/x86/cacheinfo.h
index 0f850bdf12..ee057de50d 100644
--- a/sysdeps/x86/cacheinfo.h
+++ b/sysdeps/x86/cacheinfo.h
@@ -54,6 +54,9 @@ long int __x86_rep_movsb_threshold attribute_hidden = 2048;
/* Threshold to use Enhanced REP STOSB. */
long int __x86_rep_stosb_threshold attribute_hidden = 2048;
+/* Threshold to stop using Enhanced REP MOVSB. */
+long int __x86_rep_movsb_stop_threshold attribute_hidden;
+
static void
init_cacheinfo (void)
{
@@ -85,5 +88,6 @@ init_cacheinfo (void)
__x86_rep_movsb_threshold = cpu_features->rep_movsb_threshold;
__x86_rep_stosb_threshold = cpu_features->rep_stosb_threshold;
+ __x86_rep_movsb_stop_threshold = cpu_features->rep_movsb_stop_threshold;
}
#endif
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
index 2ab3acd83e..d9944250fc 100644
--- a/sysdeps/x86/dl-cacheinfo.h
+++ b/sysdeps/x86/dl-cacheinfo.h
@@ -704,7 +704,7 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
int max_cpuid_ex;
long int data = -1;
long int shared = -1;
- long int core;
+ long int core = -1;
unsigned int threads = 0;
unsigned long int level1_icache_size = -1;
unsigned long int level1_icache_linesize = -1;
@@ -892,6 +892,18 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
#endif
}
+ unsigned long int rep_movsb_stop_threshold;
+ /* ERMS feature is implemented from AMD Zen3 architecture and it is
+ performing poorly for data above L2 cache size. Henceforth, adding
+ an upper bound threshold parameter to limit the usage of Enhanced
+ REP MOVSB operations and setting its value to L2 cache size. */
+ if (cpu_features->basic.kind == arch_kind_amd)
+ rep_movsb_stop_threshold = core;
+ /* Setting the upper bound of ERMS to the computed value of
+ non-temporal threshold for architectures other than AMD. */
+ else
+ rep_movsb_stop_threshold = non_temporal_threshold;
+
/* The default threshold to use Enhanced REP STOSB. */
unsigned long int rep_stosb_threshold = 2048;
@@ -938,4 +950,5 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
cpu_features->non_temporal_threshold = non_temporal_threshold;
cpu_features->rep_movsb_threshold = rep_movsb_threshold;
cpu_features->rep_stosb_threshold = rep_stosb_threshold;
+ cpu_features->rep_movsb_stop_threshold = rep_movsb_stop_threshold;
}
diff --git a/sysdeps/x86/include/cpu-features.h b/sysdeps/x86/include/cpu-features.h
index bfe4fe231e..74408fde5c 100644
--- a/sysdeps/x86/include/cpu-features.h
+++ b/sysdeps/x86/include/cpu-features.h
@@ -855,6 +855,8 @@ struct cpu_features
unsigned long int non_temporal_threshold;
/* Threshold to use "rep movsb". */
unsigned long int rep_movsb_threshold;
+ /* Threshold to stop using "rep movsb". */
+ unsigned long int rep_movsb_stop_threshold;
/* Threshold to use "rep stosb". */
unsigned long int rep_stosb_threshold;
/* _SC_LEVEL1_ICACHE_SIZE. */
diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
index 03a2e4dfb0..897a3d9762 100644
--- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
@@ -30,7 +30,10 @@
load and aligned store. Load the last 4 * VEC and first VEC
before the loop and store them after the loop to support
overlapping addresses.
- 6. If size >= __x86_shared_non_temporal_threshold and there is no
+ 6. On machines with ERMS feature, if size greater than equal or to
+ __x86_rep_movsb_threshold and less than
+ __x86_rep_movsb_stop_threshold, then REP MOVSB will be used.
+ 7. If size >= __x86_shared_non_temporal_threshold and there is no
overlap between destination and source, use non-temporal store
instead of aligned store. */
@@ -252,7 +255,7 @@ L(return):
#endif
L(movsb):
- cmp __x86_shared_non_temporal_threshold(%rip), %RDX_LP
+ cmp __x86_rep_movsb_stop_threshold(%rip), %RDX_LP
jae L(more_8x_vec)
cmpq %rsi, %rdi
jb 1f
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2022-05-02 21:29 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-05-02 21:29 [glibc/release/2.33/master] x86: Adding an upper bound for Enhanced REP MOVSB Sunil Pandey
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).