lkml.org 
[lkml]   [2008]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Announce: Semaphore-Removal tree
From
Date
On Sat, 2008-04-26 at 05:30 -0400, Christoph Hellwig wrote:
> On Fri, Apr 25, 2008 at 02:22:31PM -0700, Daniel Walker wrote:
> > If you can make a case for converting some semaphores to spinlocks be my
> > guest .. If you have good reasoning I wouldn't stand in the way.. (Real
> > time converts all the spinlocks to mutexes anyway ..)
>
> Right at hand I have the XFS inode hash lock was converted from a rw_semaphore
> to a rwlock_t becuase the context switch overhead was killing
> performance in various benchmarks. This is a very typical scenary for
> locks that are taken often and held for a rather short time. Add to
> that fact that a spinlock is compltely optimized away for an UP kernel
> while a mutex is not and the amount of memory that any mutex takes
> compared to a spinlock you have a clear winner.

I'm guessing RCU would be a bit more work?

The problem with rwlock_t is that for it to be a spinning lock the hold
times should be short, for it to be a rwlock over a spinlock there
should be a significant amount of concurrency, these two things together
make for a cache-line bouncing fest.





\
 
 \ /
  Last update: 2008-04-26 15:43    [W:0.047 / U:0.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site