lkml.org 
[lkml]   [2013]   [Apr]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Preemptable Ticket Spinlock
On 04/22/2013 05:56 PM, Andi Kleen wrote:
> Rik van Riel <riel@redhat.com> writes:
>>
>> If we always incremented the ticket number by 2 (instead of 1), then
>> we could use the lower bit of the ticket number as the spinlock.
>
> Spinning on a single bit is very inefficient, as you need to do
> try lock in a loop which is very unfriendly to the MESI state protocol.
> It's much better to have at least three states and allow
> spinning-while-reading-only.
>
> This is typically very visible on systems with >2S.

Absolutely, the spinning should be read-only, until the CPU
sees that the desired bit is clear. MESI-friendly spinning
is essential.

--
All rights reversed


\
 
 \ /
  Last update: 2013-04-23 01:41    [W:1.120 / U:0.072 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site