Re: [PATCH v1] perf sample: Make user_regs and intr_regs optional

[Ian Rogers]

On Mon, Jan 13, 2025 at 11:43 AM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> The struct dump_regs contains 512 bytes of cache_regs, meaning the two
> values in perf_sample contribute 1088 bytes of its total 1384 bytes
> size. Initializing this much memory has a cost reported by Tavian
> Barnes <tavianator@xxxxxxxxxxxxxx> as about 2.5% when running `perf
> script --itrace=i0`:
> https://lore.kernel.org/lkml/d841b97b3ad2ca8bcab07e4293375fb7c32dfce7.1736618095.git.tavianator@xxxxxxxxxxxxxx/
>
> Adrian Hunter <adrian.hunter@xxxxxxxxx> replied that the zero
> initialization was necessary and couldn't simply be removed.
>
> This patch aims to strike a middle ground of still zeroing the
> perf_sample, but removing 79% of its size by make user_regs and
> intr_regs optional pointers to zalloc-ed memory. To support the
> allocation accessors are created for user_regs and intr_regs. To
> support correct cleanup perf_sample__init and perf_sample__exit
> functions are created and added throughout the code base.

Ping. Given the memory savings and performance wins it would be nice
to see this land. Andi Kleen commented on doing a reimplementation,
which is fine but out-of-scope of what I'm doing here.

Thanks,
Ian