linux-kernel - Re: [PATCH 0/5] locking/lockdep: Improve lockdep performance

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Date:   Tue, 2 Oct 2018 09:57:29 -0400
From:   Waiman Long <longman@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/5] locking/lockdep: Improve lockdep performance

On 10/02/2018 05:06 AM, Ingo Molnar wrote:
> * Waiman Long <longman@...hat.com> wrote:
>
>> Enabling CONFIG_LOCKDEP and other related debug options will greatly
>> reduce system performance. This patchset aims to reduce the performance
>> slowdown caused by the lockdep code.
>>
>> Patch 1 just removes an inline function that wasn't used.
>>
>> Patches 2 and 3 are minor twists to optimize the code.
>>
>> Patch 4 makes class->ops a per-cpu counter.
>>
>> Patch 5 moves the lock_release() call outside of a lock critical section.
>>
>> Parallel kernel compilation tests (make -j <#cpu>) were performed on
>> 2 different systems:
>>
>>  1) an 1-socket 22-core 44-thread Skylake system
>>  2) a 4-socket 72-core 144-thread Broadwell system
>>
>> The build times with pre-patch and post-patch debug kernels were:
>>
>>    System      Pre-patch     Post-patch    %Change
>>    ------      ---------     ----------    -------
>>   1-socket      8m53.9s        8m41.2s      -2.4%
>>   4-socket      7m27.0s        5m31.0s      -26%
>>
>> I think it is the last 2 patches that yield most of the performance
>> improvement.
> Impressive speedup!
>
> Mind including the non-lockdep numbers as well, for reference?
>
> Thanks,
>
> 	Ingo

OK, I will include the non lockdep number for comparison. However the
debug kernel has other debugging code enabled as well so the slowdown
won't be just for the enabling of lockdep.

-Longman