lkml.org 
[lkml]   [2007]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Network slowdown due to CFS
On Mon, 1 Oct 2007 15:17:52 -0700
"David Schwartz" <davids@webmaster.com> wrote:

>
> Arjan van de Ven wrote:
>
> > > It can occasionally be an optimization. You may have a case where
> > > you can do something very efficiently if a lock is not held, but
> > > you cannot afford to wait for the lock to be released. So you
> > > check the lock, if it's held, you yield and then check again. If
> > > that fails, you do it the less optimal way (for example,
> > > dispatching it to a thread that *can* afford to wait).
>
> > at this point it's "use a futex" instead; once you're doing system
> > calls you might as well use the right one for what you're trying to
> > achieve.
>
> There are two answers to this. One is that you sometimes are writing
> POSIX code and Linux-specific optimizations don't change the fact
> that you still need a portable implementation.
>
> The other answer is that futexes don't change anything in this case.
> In fact, in the last time I hit this, the lock was a futex on Linux.
> Nevertheless, that doesn't change the basic issue. The lock is
> locked, you cannot afford to wait for it, but not getting the lock is
> expensive. The solution is to yield and check the lock again. If it's
> still held, you dispatch to another thread, but many times, yielding
> can avoid that.

yielding IS blocking. Just with indeterminate fuzzyness added to it....
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-02 00:39    [W:0.094 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site