linux-kernel - Re: [PATCH] locking/lockdep: Increase MAX_LOCKDEP

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Date:   Tue, 26 May 2020 15:28:56 -0400
From:   Qian Cai <cai@....pw>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/lockdep: Increase MAX_LOCKDEP_ENTRIES by half

On Tue, May 26, 2020 at 02:58:53PM -0400, Qian Cai wrote:
> On Tue, May 26, 2020 at 01:43:49PM -0400, Waiman Long wrote:
> > It was found by Qian Cai that lockdep splat sometimes appears with the
> > "BUG: MAX_LOCKDEP_ENTRIES too low" message on linux-next. On a 32-vcpu VM
> > guest with a v5.7-rc7 based kernel, I looked at how many of the various
> > table entries were being used after bootup and after a parallel kernel
> > build (make -j32). The tables below show the usage statistics.
> 
> I think this approach could help the situatin on this AMD server.
> However, I don't understand why this particular system starts to exceed
> the MAX_LOCKDEP_ENTRIES. All other Intel, powerpc, amd64 and s390
> running the same workload have only < 20k at the end, but on this AMD
> server,

Correction -- Intel is also quite close to exceed it.

direct dependencies:                 29836 [max: 32768]

arm64:

direct dependencies:                 25268 [max: 32768]