From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id C19056B0069 for ; Fri, 9 Dec 2016 00:16:35 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id 83so8671074pfx.1 for ; Thu, 08 Dec 2016 21:16:35 -0800 (PST) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTP id m5si31929238pgj.182.2016.12.08.21.16.34 for ; Thu, 08 Dec 2016 21:16:34 -0800 (PST) From: Byungchul Park Subject: [PATCH v4 01/15] x86/dumpstack: Optimize save_stack_trace Date: Fri, 9 Dec 2016 14:11:57 +0900 Message-Id: <1481260331-360-2-git-send-email-byungchul.park@lge.com> In-Reply-To: <1481260331-360-1-git-send-email-byungchul.park@lge.com> References: <1481260331-360-1-git-send-email-byungchul.park@lge.com> Sender: owner-linux-mm@kvack.org List-ID: To: peterz@infradead.org, mingo@kernel.org Cc: tglx@linutronix.de, walken@google.com, boqun.feng@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, npiggin@gmail.com Currently, x86 implementation of save_stack_trace() is walking all stack region word by word regardless of what the trace->max_entries is. However, it's unnecessary to walk after already fulfilling caller's requirement, say, if trace->nr_entries >= trace->max_entries is true. I measured its overhead and printed its difference of sched_clock() with my QEMU x86 machine. The latency was improved over 70% when trace->max_entries = 5. Before this patch: [ 2.329573] save_stack_trace() takes 76820 ns [ 2.329863] save_stack_trace() takes 62131 ns [ 2.330000] save_stack_trace() takes 99476 ns [ 2.329846] save_stack_trace() takes 62419 ns [ 2.330000] save_stack_trace() takes 88918 ns [ 2.330253] save_stack_trace() takes 73669 ns [ 2.330520] save_stack_trace() takes 67876 ns [ 2.330671] save_stack_trace() takes 75963 ns [ 2.330983] save_stack_trace() takes 95079 ns [ 2.330451] save_stack_trace() takes 62352 ns After this patch: [ 2.795000] save_stack_trace() takes 21147 ns [ 2.795397] save_stack_trace() takes 20230 ns [ 2.795397] save_stack_trace() takes 31274 ns [ 2.795739] save_stack_trace() takes 19706 ns [ 2.796484] save_stack_trace() takes 20266 ns [ 2.796484] save_stack_trace() takes 20902 ns [ 2.797000] save_stack_trace() takes 38110 ns [ 2.797510] save_stack_trace() takes 20224 ns [ 2.798181] save_stack_trace() takes 20172 ns [ 2.798837] save_stack_trace() takes 20824 ns Signed-off-by: Byungchul Park --- arch/x86/include/asm/stacktrace.h | 1 + arch/x86/kernel/dumpstack.c | 4 ++++ arch/x86/kernel/dumpstack_32.c | 2 ++ arch/x86/kernel/stacktrace.c | 7 +++++++ 4 files changed, 14 insertions(+) diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h index 0944218..f6d0694 100644 --- a/arch/x86/include/asm/stacktrace.h +++ b/arch/x86/include/asm/stacktrace.h @@ -41,6 +41,7 @@ struct stacktrace_ops { /* On negative return stop dumping */ int (*stack)(void *data, char *name); walk_stack_t walk_stack; + int (*end_walk)(void *data); }; void dump_trace(struct task_struct *tsk, struct pt_regs *regs, diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index ef8017c..274d42a 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -113,6 +113,8 @@ print_context_stack(struct task_struct *task, print_ftrace_graph_addr(addr, data, ops, task, graph); } stack++; + if (ops->end_walk && ops->end_walk(data)) + break; } return bp; } @@ -138,6 +140,8 @@ print_context_stack_bp(struct task_struct *task, frame = frame->next_frame; ret_addr = &frame->return_address; print_ftrace_graph_addr(addr, data, ops, task, graph); + if (ops->end_walk && ops->end_walk(data)) + break; } return (unsigned long)frame; diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c index fef917e..762d1fd 100644 --- a/arch/x86/kernel/dumpstack_32.c +++ b/arch/x86/kernel/dumpstack_32.c @@ -69,6 +69,8 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs, bp = ops->walk_stack(task, stack, bp, ops, data, end_stack, &graph); + if (ops->end_walk && ops->end_walk(data)) + break; /* Stop if not on irq stack */ if (!end_stack) diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c index 9ee98ee..a44de4d 100644 --- a/arch/x86/kernel/stacktrace.c +++ b/arch/x86/kernel/stacktrace.c @@ -47,10 +47,17 @@ save_stack_address_nosched(void *data, unsigned long addr, int reliable) return __save_stack_address(data, addr, reliable, true); } +static int save_stack_end(void *data) +{ + struct stack_trace *trace = data; + return trace->nr_entries >= trace->max_entries; +} + static const struct stacktrace_ops save_stack_ops = { .stack = save_stack_stack, .address = save_stack_address, .walk_stack = print_context_stack, + .end_walk = save_stack_end, }; static const struct stacktrace_ops save_stack_ops_nosched = { -- 1.9.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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