From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755227Ab1FONwj (ORCPT ); Wed, 15 Jun 2011 09:52:39 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.123]:52981 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754857Ab1FONwg (ORCPT ); Wed, 15 Jun 2011 09:52:36 -0400 X-Authority-Analysis: v=1.1 cv=IOX921YOuPvYFce5aSLzPVIStpiCPR9M8R83dyHW74w= c=1 sm=0 a=vhdKIqpQuCYA:10 a=uNyXQxNb8OMA:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=1XWaLZrsAAAA:8 a=pGLkceISAAAA:8 a=20KFwNOVAAAA:8 a=Z4Rwk6OoAAAA:8 a=VwQbUJbxAAAA:8 a=meVymXHHAAAA:8 a=hQU54lLi4O9_Ju9IwBkA:9 a=vQ4IctnvpC4Kuc3l088A:7 a=UTB_XpHje0EA:10 a=MSl-tDqOz04A:10 a=jEp0ucaQiEUA:10 a=jbrJJM5MRmoA:10 a=jeBq3FmKZ4MA:10 a=dkb_eO1BMdooRQXa:21 a=S1wD_cfDYDu4SM5X:21 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Message-Id: <20110615135232.815913675@goodmis.org> User-Agent: quilt/0.48-1 Date: Wed, 15 Jun 2011 09:48:42 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Masami Hiramatsu , Vaibhav Nagarnaik , Frederic Weisbecker , Ingo Molnar , Michael Rubin , David Sharp , Linus Torvalds Subject: [PATCH 01/16 v2] tracing: Schedule a delayed work to call wakeup() References: <20110615134841.767565350@goodmis.org> Content-Disposition: inline; filename=0001-tracing-Schedule-a-delayed-work-to-call-wakeup.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vaibhav Nagarnaik In using syscall tracing by concurrent processes, the wakeup() that is called in the event commit function causes contention on the spin lock of the waitqueue. I enabled sys_enter_getuid and sys_exit_getuid tracepoints, and by running getuid_microbench from autotest in parallel I found that the contention causes exponential latency increase in the tracing path. The autotest binary getuid_microbench calls getuid() in a tight loop for the given number of iterations and measures the average time required to complete a single invocation of syscall. The patch schedules a delayed work after 2 ms once an event commit calls to wake up the trace wait_queue. This removes the delay caused by contention on spin lock in wakeup() and amortizes the wakeup() calls scheduled over the 2 ms period. In the following example, the script enables the sys_enter_getuid and sys_exit_getuid tracepoints and runs the getuid_microbench in parallel with the given number of processes. The output clearly shows the latency increase caused by contentions. $ ~/getuid.sh 1 1000000 calls in 0.720974253 s (720.974253 ns/call) $ ~/getuid.sh 2 1000000 calls in 1.166457554 s (1166.457554 ns/call) 1000000 calls in 1.168933765 s (1168.933765 ns/call) $ ~/getuid.sh 3 1000000 calls in 1.783827516 s (1783.827516 ns/call) 1000000 calls in 1.795553270 s (1795.553270 ns/call) 1000000 calls in 1.796493376 s (1796.493376 ns/call) $ ~/getuid.sh 4 1000000 calls in 4.483041796 s (4483.041796 ns/call) 1000000 calls in 4.484165388 s (4484.165388 ns/call) 1000000 calls in 4.484850762 s (4484.850762 ns/call) 1000000 calls in 4.485643576 s (4485.643576 ns/call) $ ~/getuid.sh 5 1000000 calls in 6.497521653 s (6497.521653 ns/call) 1000000 calls in 6.502000236 s (6502.000236 ns/call) 1000000 calls in 6.501709115 s (6501.709115 ns/call) 1000000 calls in 6.502124100 s (6502.124100 ns/call) 1000000 calls in 6.502936358 s (6502.936358 ns/call) After the patch, the latencies scale better. 1000000 calls in 0.728720455 s (728.720455 ns/call) 1000000 calls in 0.842782857 s (842.782857 ns/call) 1000000 calls in 0.883803135 s (883.803135 ns/call) 1000000 calls in 0.902077764 s (902.077764 ns/call) 1000000 calls in 0.902838202 s (902.838202 ns/call) 1000000 calls in 0.908896885 s (908.896885 ns/call) 1000000 calls in 0.932523515 s (932.523515 ns/call) 1000000 calls in 0.958009672 s (958.009672 ns/call) 1000000 calls in 0.986188020 s (986.188020 ns/call) 1000000 calls in 0.989771102 s (989.771102 ns/call) 1000000 calls in 0.933518391 s (933.518391 ns/call) 1000000 calls in 0.958897947 s (958.897947 ns/call) 1000000 calls in 1.031038897 s (1031.038897 ns/call) 1000000 calls in 1.089516025 s (1089.516025 ns/call) 1000000 calls in 1.141998347 s (1141.998347 ns/call) Signed-off-by: Vaibhav Nagarnaik Cc: Frederic Weisbecker Cc: Ingo Molnar Cc: Michael Rubin Cc: David Sharp Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1305059241-7629-1-git-send-email-vnagarnaik@google.com Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 23 ++++++++++++----------- 1 files changed, 12 insertions(+), 11 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ee9c921..71777c8 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -343,26 +343,27 @@ unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK | static int trace_stop_count; static DEFINE_SPINLOCK(tracing_start_lock); +static void wakeup_work_handler(struct work_struct *work) +{ + wake_up(&trace_wait); +} + +static DECLARE_DELAYED_WORK(wakeup_work, wakeup_work_handler); + /** * trace_wake_up - wake up tasks waiting for trace input * - * Simply wakes up any task that is blocked on the trace_wait - * queue. These is used with trace_poll for tasks polling the trace. + * Schedules a delayed work to wake up any task that is blocked on the + * trace_wait queue. These is used with trace_poll for tasks polling the + * trace. */ void trace_wake_up(void) { - int cpu; + const unsigned long delay = msecs_to_jiffies(2); if (trace_flags & TRACE_ITER_BLOCK) return; - /* - * The runqueue_is_locked() can fail, but this is the best we - * have for now: - */ - cpu = get_cpu(); - if (!runqueue_is_locked(cpu)) - wake_up(&trace_wait); - put_cpu(); + schedule_delayed_work(&wakeup_work, delay); } static int __init set_buf_size(char *str) -- 1.7.4.4