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Date: Fri, 18 Mar 2022 14:12:39 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>,
Byungchul Park <byungchul.park@....com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Arnd Bergmann <arnd@...db.de>,
Radoslaw Burny <rburny@...gle.com>,
linux-arch <linux-arch@...r.kernel.org>,
bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH 0/2] locking: Add new lock contention tracepoints (v3)
Hello Hyeonggon,
On Thu, Mar 17, 2022 at 10:32 AM Hyeonggon Yoo <42.hyeyoo@...il.com> wrote:
>
> On Wed, Mar 16, 2022 at 03:45:46PM -0700, Namhyung Kim wrote:
> > Hello,
> >
> > There have been some requests for low-overhead kernel lock contention
> > monitoring. The kernel has CONFIG_LOCK_STAT to provide such an infra
> > either via /proc/lock_stat or tracepoints directly.
> >
> > However it's not light-weight and hard to be used in production. So
> > I'm trying to add new tracepoints for lock contention and using them
> > as a base to build a new monitoring system.
>
> Hello Namhyung,
> I like this series so much.
> Lock contentions became much more visible without serious overhead.
>
> For the series:
> Tested-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
Thanks!
>
> How would you use these tracepoints, is there a script you use?
Not yet. But I'm thinking something similar to your script.
Probably I'll extend 'perf lock' command to have this kind of output
but it doesn't have lock name and use avg/min/max time instead of
histogram.
Thanks,
Namhyung
> For testing, I just wrote a simple bpftrace script:
>
> $ sudo bpftrace -e 'BEGIN
> {
> printf("Collecting lockstats... Hit Ctrl-C to end.\n");
> }
>
> tracepoint:lock:contention_begin
> {
> @start_us[tid] = nsecs / 1000;
> }
>
> tracepoint:lock:contention_end
> {
> if (args->ret == 0) {
> @stats[kstack] = hist(nsecs / 1000 - @start_us[tid]);
> }
> }
>
> END
> {
> clear(@start_us);
> }'
>
> And it shows its distribution of slowpath wait time like below. Great.
>
> @stats[
> __traceiter_contention_end+76
> __traceiter_contention_end+76
> queued_spin_lock_slowpath+556
> _raw_spin_lock+108
> rmqueue_bulk+80
> rmqueue+1060
> get_page_from_freelist+372
> __alloc_pages+208
> alloc_pages_vma+160
> alloc_zeroed_user_highpage_movable+72
> do_anonymous_page+92
> handle_pte_fault+320
> __handle_mm_fault+252
> handle_mm_fault+244
> do_page_fault+340
> do_translation_fault+100
> do_mem_abort+76
> el0_da+60
> el0t_64_sync_handler+232
> el0t_64_sync+420
> ]:
> [2, 4) 1 |@ |
> [4, 8) 30 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [8, 16) 25 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [16, 32) 33 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [32, 64) 29 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [64, 128) 13 |@@@@@@@@@@@@@@@@@@@@ |
> [128, 256) 2 |@@@ |
>
>
> @stats[
> __traceiter_contention_end+76
> __traceiter_contention_end+76
> rwsem_down_write_slowpath+1216
> down_write_killable+100
> do_mprotect_pkey.constprop.0+176
> __arm64_sys_mprotect+40
> invoke_syscall+80
> el0_svc_common.constprop.0+76
> do_el0_svc+52
> el0_svc+48
> el0t_64_sync_handler+164
> el0t_64_sync+420
> ]:
> [1] 13 |@@@@@@@@@@@ |
> [2, 4) 42 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [4, 8) 5 |@@@@ |
> [8, 16) 10 |@@@@@@@@ |
> [16, 32) 60 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [32, 64) 41 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [64, 128) 40 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [128, 256) 14 |@@@@@@@@@@@@ |
> [256, 512) 7 |@@@@@@ |
> [512, 1K) 6 |@@@@@ |
> [1K, 2K) 2 |@ |
> [2K, 4K) 1 | |
>
> @stats[
> __traceiter_contention_end+76
> __traceiter_contention_end+76
> queued_spin_lock_slowpath+556
> _raw_spin_lock+108
> futex_wake+168
> do_futex+200
> __arm64_sys_futex+112
> invoke_syscall+80
> el0_svc_common.constprop.0+76
> do_el0_svc+52
> el0_svc+48
> el0t_64_sync_handler+164
> el0t_64_sync+420
> ]:
> [0] 3 | |
> [1] 2515 |@ |
> [2, 4) 8747 |@@@@@ |
> [4, 8) 17052 |@@@@@@@@@@ |
> [8, 16) 46706 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [16, 32) 82105 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
> [32, 64) 46918 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ |
> [64, 128) 99 | |
> [128, 256) 1 | |
> [256, 512) 8 | |
> [512, 1K) 0 | |
> [1K, 2K) 0 | |
> [2K, 4K) 0 | |
> [4K, 8K) 0 | |
> [8K, 16K) 0 | |
> [16K, 32K) 5 | |
> [32K, 64K) 12 | |
> [64K, 128K) 34 | |
> [128K, 256K) 68 | |
> [256K, 512K) 7 | |
>
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