Re: [PATCH 3/3] arm64: use runtime constant to optimize handle_arch_irq access

[Leo Yan <leo.yan@arm.com>]

Hi Jisheng,

On Fri, Feb 20, 2026 at 05:09:22PM +0800, Jisheng Zhang wrote:
> Currently, on arm64 platforms, the handle_arch_irq is a pointer which
> is set during booting, and every irq processing needs to access it,
> so it sits in hot code path. We can use the runtime constant mechanism
> which was introduced by Linus to speed up its accessing.
> 
> Tested on Quad CA55 platform, the perf sched benchmark is improved
> by ~6.5%

6.5% is a quite high margin, especially for only one pointer's change.
Maybe it is good to share more info for which compiler you are using,
how you tested and the detailed results.

I played a bit on my juno board on CA73 cores with the command:

  perf bench sched all

Run 3 iterations, and measures three metrics (messaging/pipe/seccomp)
and results in seconds. Less is better.

  +---------------------+--------+--------+--------+--------+
  |Without change       |   run1 |   run2 |   run3 |    avg |
  +---------------------+--------+--------+--------+--------+
  |messaging (sec)      |  4.546 |  4.508 |  4.591 |  4.548 |
  |pipe (sec)           | 24.258 | 24.224 | 24.017 | 24.166 |
  |seccomp-notify (sec) | 48.393 | 48.457 | 48.232 | 48.361 |
  +---------------------+--------+--------+--------+--------+

  +---------------------+--------+--------+--------+--------+--------+
  |With change          |   run1 |   run2 |   run3 |    avg |   diff |
  +---------------------+--------+--------+--------+--------+--------+
  |messaging (sec)      |  4.493 |  4.523 |  4.556 |  4.524 | +0.52% |
  |pipe (sec)           | 23.159 | 23.702 | 28.649 | 25.170 | -4.15% |
  |seccomp-notify (sec) | 46.848 | 46.938 | 46.973 | 46.920 | +2.98% |
  +---------------------+--------+--------+--------+--------+--------+

With this patch, the messaging test shows a minor improvement (0.52%).

The pipe test performs worse (-4.15%) after applying the patch. However,
one positive signal is that the minimum latency is 23.159, which is
lower than without the change (24.017).

For seccomp, the results indicate a benefit (2.98%) from the change.

Hope this is helpful for maintainers to judge the change.

I'd leave maintainers to review the code.

Thanks,
Leo