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

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Date:   Tue, 26 May 2020 16:17:39 -0400
From:   Qian Cai <cai@....pw>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, 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 09:56:30PM +0200, Peter Zijlstra wrote:
> On Tue, May 26, 2020 at 02:58:50PM -0400, Qian Cai wrote:
> 
> > I still don't understand why reading all sysfs files on this system
> > could increase that much, but here is the lockdep file after
> > running sysfs read to see if you could spot anything obviously,
> > 
> > https://cailca.github.io/files/lockdep.txt
> 
> 00000000f011a2a5 OPS:      20 FD:   45 BD:    1 .+.+: kn->active#834
> 
> is that somewhere near the number of CPUs you have?

834? No.

# lscpu
Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              128
On-line CPU(s) list: 0-127
Thread(s) per core:  2
Core(s) per socket:  32
Socket(s):           2
NUMA node(s):        8
Vendor ID:           AuthenticAMD
CPU family:          23
Model:               1
Model name:          AMD EPYC 7601 32-Core Processor
Stepping:            2
CPU MHz:             2932.801
CPU max MHz:         2200.0000
CPU min MHz:         1200.0000
BogoMIPS:            4391.87
Virtualization:      AMD-V
L1d cache:           32K
L1i cache:           64K
L2 cache:            512K
L3 cache:            8192K
NUMA node0 CPU(s):   0-7,64-71
NUMA node1 CPU(s):   8-15,72-79
NUMA node2 CPU(s):   16-23,80-87
NUMA node3 CPU(s):   24-31,88-95
NUMA node4 CPU(s):   32-39,96-103
NUMA node5 CPU(s):   40-47,104-111
NUMA node6 CPU(s):   48-55,112-119
NUMA node7 CPU(s):   56-63,120-127

> 
> Anyway, there's very long "kn->active#..." chains in there, which seems
> to suggest some annotation is all sorts of buggered.