[lkml]   [2019]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 01/25] x86: Make SMAP 64-bit only
On March 18, 2019 11:10:22 AM PDT, Linus Torvalds <> wrote:
>On Mon, Mar 18, 2019 at 10:51 AM Peter Zijlstra <>
>> How about I do a patch that schedules EFLAGS for both 32bit and
>> mark this for backporting to infinity.
>> And then at the end, after the objtool-ac bits land, I do a patch
>> removing the EFLAGS scheduling for x86_64.
>Sounds sane to me.
>And we can make it AC-conditional if it's actually shown to be visible
>from a performance standpoint.
>But iirc pushf/popf isn't really that expensive - in fact I think it's
>pretty cheap when system flags don't change. Which would be the common
>case unless you'd also make the popf do the irq restore part and
>simply make finish_lock_switch() re-enable irq's by doing an
>I think popf is like 20 cycles or something (and pushf is just single
>cycles). Probably not worth worrying about in the task switch context.
> Linus

Yes, the problem isn't scheduling per se but the risk of hiding problems.
Sent from my Android device with K-9 Mail. Please excuse my brevity.

 \ /
  Last update: 2019-03-21 18:13    [W:0.085 / U:4.316 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site