linux-kernel - Re: [PATCH 1/2] sched/wait: Break up long wake list walk

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Message-ID: <CA+55aFwzTMrZwh7TE_VeZt8gx5Syoop-kA=Xqs56=FkyakrM6g@mail.gmail.com>
Date:   Thu, 17 Aug 2017 09:25:08 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk

On Thu, Aug 17, 2017 at 9:17 AM, Liang, Kan <kan.liang@...el.com> wrote:
>
> We tried both 12 and 16 bit table and that didn't make a difference.
> The long wake ups are mostly on the same page when we do instrumentation

Ok.

> Here is the wake_up_page_bit call stack when the workaround is running, which
> is collected by perf record -g -a -e probe:wake_up_page_bit -- sleep 10

It's actually not really wake_up_page_bit() that is all that
interesting, it would be more interesting to see which path it is that
*adds* the entries.

So it's mainly wait_on_page_bit_common(), but also add_page_wait_queue().

Can you get that call stack instead (or in addition to)?

                  Linus