Re: [PATCH v2 07/14] perf arm-spe: Use generic snapshot search

[sashiko-bot@kernel.org]

> The new generic snapshot search gives a similar result as the
> reimplemented version of it here. One slight difference is in the
> pointer fixup. SPE has:
> 
>   *head += mm->len;
>   *old = *head - mm->len;
> 
> Which gives exactly the same result but written in reverse order to the
> generic one:
> 
>   *old = *head;
>   *head += mm->len;
> 
> SPE also had a special fixup case for head pointers greater than the
> buffer length, which is not needed because the SPE driver always wraps
> them, and __auxtrace_mmap__read() handles that anyway. It also didn't
> have the special case for old > head for when the wrap heuristic fails
> but the pointers showed a wrap had happened.
> 
> The other feature lost is that this search only looked from head to the
> end of the buffer, rather than always at the last 512 bytes. This was
> flawed because once head is close to the end, it's likely it could
> contain zero padding from actual SPE data and a wrap would be missed.
> It's better to err on the side of caution and mark as a wrap, rather
> than trying to optimize by limiting the search from head onwards.
> 
> Signed-off-by: James Clark <james.clark@linaro.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260821-james-cs-unformatted-per-thread-fix-v2-0-00c4fd0701b4@linaro.org?part=7