[lkml]   [2009]   [Jan]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH -v5][RFC]: mutex: implement adaptive spinning

On Wed, 7 Jan 2009, Gregory Haskins wrote:
> Can I ask a simple question in light of all this discussion?
> "Is get_task_struct() really that bad?"

Yes. It's an atomic access (two, in fact, since you need to release it
too), which is a huge deal if we're talking about a timing-critical
section of code.

And this is timing-critical, or we wouldn't even care - even in the
contention case. Admittedly btrfs apparently makes it more so that it
_should_ be, but Peter had some timings that happened with just regular
create/unlink that showed a big difference.

So the whole and only point of spinning mutexes is to get rid of the
scheduler overhead, but to also not replace it with some other thing ;)


 \ /
  Last update: 2009-01-08 00:21    [W:0.155 / U:27.072 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site