lkml.org 
[lkml]   [2022]   [May]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [mm/page_alloc] f26b3fa046: netperf.Throughput_Mbps -18.0% regression
On Tue, May 10, 2022 at 12:03 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I think the PV case already basically does that - replacing the the
> "store release" with a much more complex sequence. No?

Looking around, the PV case is absolutely horrid, and does a
cmpxchg_release() on the unlock path. Yeah, that would make the unlock
*much* more expensive.

And I guess that's fairly fundamental. Even if you were to avoid an
explicitly atomic access - do the unlock a non-atomic write followed
by a non-atomic "read pending and see if we need to something
expensive", just that check would have to involve at a minimum a
memory barrier, so it ends up being expensive even for the
non-contended case.

Linus

\
 
 \ /
  Last update: 2022-05-10 21:26    [W:0.091 / U:0.828 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site