Re: [PATCH v3 10/11] zram: use rw_semaphore for decompression streams

[Sergey Senozhatsky]

On (26/10/16 21:48), Bo Zhang wrote:
> On Fri, 16 Oct 2026 17:54:25 +0900 Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> wrote:
> > A quick and dirty patch, as usual, just to play around with.  This
> > attempts to improve the reader side, because the reader is side
> > much more sensitive.  Tested only with zstd.
> 
> I applied the cross-CPU borrowing patch on-device and re-ran the same
> zstd Android A/B, so it can be compared against the preempt-disable
> numbers I posted earlier. Focusing on the read (exclusive decompression)
> side, which is what this patch targets:
> 
>                         9+10+kmalloc   preempt-disable   cross-CPU borrow
>   dexcl_contended       15,919         54                1,447
>   dexcl_wait_ns_total   109.6 s        0.68 s            3.66 s
>   dexcl_wait_ns_max     145 ms         34.6 ms           26.6 ms
>   dexcl_avg_wait        6.88 ms        12.6 ms           2.53 ms
>   dexcl_acquire         2.21M          2.75M             2.94M
> 
> Borrowing clearly works: dexcl contention drops 15,919 -> 1,447 (-91%),
> and the residual 1,447 are the genuinely all-CPUs-busy cases that fall
> through to wait_event(). More importantly for us, the worst case and the
> average are the best of the three - max 145ms -> 26.6ms (-82%), avg down
> to 2.53ms.

Thank you Bo!  I included your numbers into the commit message.