linux-kernel - Re: [PATCH v2 2/2] debugobjects: Disable lockdep tracking of debugobjects internal locks

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Message-ID: <52e6048f-c361-e6bc-7840-a55bbd30416f@redhat.com>
Date:   Fri, 28 Sep 2018 14:33:40 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Arnd Bergmann <arnd@...db.de>, chuhu@...hat.com
Subject: Re: [PATCH v2 2/2] debugobjects: Disable lockdep tracking of
 debugobjects internal locks

On 09/25/2018 12:36 PM, Waiman Long wrote:
> On 09/25/2018 12:31 PM, Peter Zijlstra wrote:
>> Also, where is the performance benefit here. The normal lock_acquire
>> path doesn't change gobal state (it will not see new lock ordering in
>> 99%+ of the cases).
>>
>> Typically we only push the lock on the task local lock stack, compute
>> the new hash, and do the hash lookup, find it already exists and return.
>>
>> So what is the expensive part, and can we do something about that?
> I will need to do some experimentation to find out. Will update this
> thread with my finding.
>

I have sent out a patchset on improving lockdep performance that
hopefully will help to alleviate the problems that I saw. I still have
other ideas about further changes I want to investigate, but that will
wait until I am done with the current lockdep patchset.

-Longman