From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 5693 invoked by alias); 18 Dec 2009 18:10:51 -0000 Received: (qmail 5673 invoked by uid 22791); 18 Dec 2009 18:10:49 -0000 X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 18 Dec 2009 18:10:43 +0000 Received: from int-mx04.intmail.prod.int.phx2.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.17]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nBIIAfYx024185 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Fri, 18 Dec 2009 13:10:41 -0500 Received: from dhcp-100-2-132.bos.redhat.com (dhcp-100-2-132.bos.redhat.com [10.16.2.132]) by int-mx04.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id nBIIAdZD001703; Fri, 18 Dec 2009 13:10:40 -0500 From: Masami Hiramatsu Subject: [PATCH -tip v7 00/11] kprobes: Kprobes jump optimization support To: Frederic Weisbecker , Ingo Molnar , Ananth N Mavinakayanahalli , lkml Cc: systemtap, DLE Date: Fri, 18 Dec 2009 18:10:00 -0000 Message-ID: <20091218181527.21350.45287.stgit@dhcp-100-2-132.bos.redhat.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2009-q4/txt/msg00976.txt.bz2 Hi, Here are the patchset of the kprobes jump optimization v7 (a.k.a. Djprobe). This version is just moving onto 2.6.33-rc1-tip. Ingo, I assume its a good timing to push this code onto -tip tree (maybe developing branch?), since people can test it with perf-probe. I made a separated patch of generic text_poke_smp() for cross modifying code(XMC) by using stop_machine(), which originally comes from Mathieu's immediate value code. Thanks Mathieu, for helping me to implement it and organizing discussion points about int3-base XMC! These patches can be applied on the latest -tip. Changes in v7: - Remove ctl_name = CTL_UNNUMBERED for upstream compatibility. And kprobe stress test didn't found any regressions - from kprobes, under kvm/x86. TODO: - Support preemptive kernel (by stack unwinding and checking address). Jump Optimized Kprobes ====================== o Concept Kprobes uses the int3 breakpoint instruction on x86 for instrumenting probes into running kernel. Jump optimization allows kprobes to replace breakpoint with a jump instruction for reducing probing overhead drastically. o Performance An optimized kprobe 5 times faster than a kprobe. Optimizing probes gains its performance. Usually, a kprobe hit takes 0.5 to 1.0 microseconds to process. On the other hand, a jump optimized probe hit takes less than 0.1 microseconds (actual number depends on the processor). Here is a sample overheads. Intel(R) Xeon(R) CPU E5410 @ 2.33GHz (without debugging options) x86-32 x86-64 kprobe: 0.68us 0.91us kprobe+booster: 0.27us 0.40us kprobe+optimized: 0.06us 0.06us kretprobe : 0.95us 1.21us kretprobe+booster: 0.53us 0.71us kretprobe+optimized: 0.30us 0.35us (booster skips single-stepping) Note that jump optimization also consumes more memory, but not so much. It just uses ~200 bytes, so, even if you use ~10,000 probes, it just consumes a few MB. o Usage Set CONFIG_OPTPROBES=y when building a kernel, then all *probes will be optimized if possible. Kprobes decodes probed function and checks whether the target instructions can be optimized(replaced with a jump) safely. If it can't be, Kprobes just doesn't optimize it. o Optimization Before preparing optimization, Kprobes inserts original(user-defined) kprobe on the specified address. So, even if the kprobe is not possible to be optimized, it just uses a normal kprobe. - Safety check First, Kprobes gets the address of probed function and checks whether the optimized region, which will be replaced by a jump instruction, does NOT straddle the function boundary, because if the optimized region reaches the next function, its caller causes unexpected results. Next, Kprobes decodes whole body of probed function and checks there is NO indirect jump, NO instruction which will cause exception by checking exception_tables (this will jump to fixup code and fixup code jumps into same function body) and NO near jump which jumps into the optimized region (except the 1st byte of jump), because if some jump instruction jumps into the middle of another instruction, it causes unexpected results too. Kprobes also measures the length of instructions which will be replaced by a jump instruction, because a jump instruction is longer than 1 byte, it may replaces multiple instructions, and it checks whether those instructions can be executed out-of-line. - Preparing detour code Then, Kprobes prepares "detour" buffer, which contains exception emulating code (push/pop registers, call handler), copied instructions(Kprobes copies instructions which will be replaced by a jump, to the detour buffer), and a jump which jumps back to the original execution path. - Pre-optimization After preparing detour code, Kprobes enqueues the kprobe to optimizing list and kicks kprobe-optimizer workqueue to optimize it. To wait other optimized probes, kprobe-optimizer will delay to work. When the optimized-kprobe is hit before optimization, its handler changes IP(instruction pointer) to copied code and exits. So, the instructions which were copied to detour buffer are executed on the detour buffer. - Optimization Kprobe-optimizer doesn't start instruction-replacing soon, it waits synchronize_sched for safety, because some processors are possible to be interrupted on the middle of instruction series (2nd or Nth instruction) which will be replaced by a jump instruction(*). As you know, synchronize_sched() can ensure that all interruptions which were executed when synchronize_sched() was called are done, only if CONFIG_PREEMPT=n. So, this version supports only the kernel with CONFIG_PREEMPT=n.(**) After that, kprobe-optimizer replaces the 4 bytes right after int3 breakpoint with relative-jump destination, and synchronize caches on all processors. Next, it replaces int3 with relative-jump opcode, and synchronize caches again. - Unoptimization When unregistering, disabling kprobe or being blocked by other kprobe, an optimized-kprobe will be unoptimized. Before kprobe-optimizer runs, the kprobe just be dequeued from the optimized list. When the optimization has been done, it replaces a jump with int3 breakpoint and original code. First it puts int3 at the first byte of the jump, synchronize caches on all processors, and replaces the 4 bytes right after int3 with the original code. (*)Please imagine that 2nd instruction is interrupted and stop_machine() replaces the 2nd instruction with jump *address* while running interrupt handler. When the interrupt returns to original address, there is no valid instructions and it causes unexpected result. (**)This optimization-safety checking may be replaced with stop-machine method which ksplice is done for supporting CONFIG_PREEMPT=y kernel. Thank you, --- Masami Hiramatsu (11): [RFC] kprobes/x86: Use text_poke_fixup() for jump optimization [RFC] x86: Introduce generic jump patching without stop_machine kprobes: Add documents of jump optimization kprobes/x86: Support kprobes jump optimization on x86 x86: Add text_poke_smp for SMP cross modifying code kprobes/x86: Cleanup save/restore registers kprobes/x86: Boost probes when reentering kprobes: Jump optimization sysctl interface kprobes: Introduce kprobes jump optimization kprobes: Introduce generic insn_slot framework kprobes/x86: Cleanup RELATIVEJUMP_INSTRUCTION to RELATIVEJUMP_OPCODE Documentation/kprobes.txt | 192 ++++++++++- arch/Kconfig | 13 + arch/x86/Kconfig | 1 arch/x86/include/asm/alternative.h | 15 + arch/x86/include/asm/kprobes.h | 31 ++ arch/x86/kernel/alternative.c | 162 +++++++++ arch/x86/kernel/kprobes.c | 592 ++++++++++++++++++++++++++++------ include/linux/kprobes.h | 44 +++ kernel/kprobes.c | 628 +++++++++++++++++++++++++++++++----- kernel/sysctl.c | 12 + 10 files changed, 1484 insertions(+), 206 deletions(-) -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com