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From: Thomas Gleixner <tglx@kernel.org>
To: Shrikanth Hegde <sshegde@linux.ibm.com>, LKML
 <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Michael Kelley <mhklinux@outlook.com>, Dmitry Ilvokhin
 <d@ilvokhin.com>, Radu Rendec <radu@rendec.net>, Jan Kiszka
 <jan.kiszka@siemens.com>, Kieran Bingham <kbingham@kernel.org>, Florian
 Fainelli <florian.fainelli@broadcom.com>, Marc Zyngier <maz@kernel.org>
Subject: Re: [patch V6 00/16] Improve /proc/interrupts further
In-Reply-To: <e123b8b9-a179-48fa-9e48-2bfcbcc24b86@linux.ibm.com>
References: <20260517194421.705253664@kernel.org>
 <e123b8b9-a179-48fa-9e48-2bfcbcc24b86@linux.ibm.com>
Date: Wed, 20 May 2026 17:27:03 +0200
Message-ID: <87wlwyw188.ffs@tglx>
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Shrikanth!

On Wed, May 20 2026 at 02:48, Shrikanth Hegde wrote:
> On 5/18/26 1:31 AM, Thomas Gleixner wrote:
>
> Ran perf stat -r 1000 cat /proc/interrupts > tmp.txt
> and Observed minimal improvement with series.

Can you redirect it to /dev/null instead to take the file operations out
of the picture?

> Base:
>           1,313,263      cycles:HG                        #    4.063 GHz                         ( +-  0.17% )
>           2,172,511      instructions:HG                  #    1.65  insn per cycle              ( +-  0.05% )

> v6 series:
>           1,224,666      cycles:HG                        #    4.058 GHz                         ( +-  0.25% )
>           1,667,435      instructions:HG                  #    1.36  insn per cycle              ( +-  0.08% )

Interesting. The number of instructions goes down by 20+%, but at the
same time IPC drops too.

> Looking at powerpc arch_show_interrupts,
> It could use the similar set of optimizations.
> - move to array based
> - use irq_proc_emit_counts
> - some interrupts such as machine check, is hardly set. set skip_vector.
>
>
> Copilot suggested below diff to quickly try irq_proc_emit_counts integration.
> It showed little gains compared to v6. So it maybe worth fixing that in the
> right way. (similar to x86 stuff you have done)
>
>   Performance counter stats for 'cat /proc/interrupts' (1000 runs):
>
>                0.29 msec task-clock:HG                    #    0.586 CPUs utilized               ( +-  0.22% )
>                   0      context-switches:HG              #    0.000 /sec
>                   0      cpu-migrations:HG                #    0.000 /sec
>                  44      page-faults:HG                   #  153.067 K/sec                       ( +-  0.03% )
>           1,166,567      cycles:HG                        #    4.058 GHz                         ( +-  0.22% )
>           1,475,365      instructions:HG                  #    1.26  insn per cycle              ( +-  0.09% )
>             249,051      branches:HG                      #  866.397 M/sec                       ( +-  0.10% )
>               5,104      branch-misses:HG                 #    2.05% of all branches             ( +-  0.33% )
>
>         0.000490211 +- 0.000000992 seconds time elapsed  ( +-  0.20% )   <<< 3-4% improvements.

Again IPC drops ....