linux-kernel - Re: [PATCH 1/2] locking/qspinlock_stat: Count instances of nested lock slowpaths

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Message-ID: <20181017073833.GE3121@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Oct 2018 09:38:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] locking/qspinlock_stat: Count instances of nested
 lock slowpaths

On Tue, Oct 16, 2018 at 09:45:06AM -0400, Waiman Long wrote:
> Queued spinlock supports up to 4 levels of lock slowpath nesting -
> user context, soft IRQ, hard IRQ and NMI. However, we are not sure how
> often the nesting happens. So 3 more per-cpu stat counters are added
> to track the number of instances where nesting index goes to 1, 2 and
> 3 respectively.
> 
> On a dual-socket 64-core 128-thread Zen server, the following were stat
> counter values under different circumstances.
> 
>          State                      slowpath   index1   index2   index3
>          -----                      --------   ------   ------   -------
>   After bootup                      1,012,150    82       0        0
>   After parallel build + perf-top 125,195,009    82       0        0

Would probably be good to check a network workload.