Re: NFS client latencies

Lee Revell
2005-04-01T02:28:39Z

On Thu, 2005-03-31 at 16:50 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
>
> > > So the overhead you are currently seeing should just be that of
> > > iterating through the list, locking said requests and adding them to
> > > our private list.
> >
> > ah - cool! This was a 100 MB writeout so having 3.7 msecs to process
> > 20K+ pages is not unreasonable. To break the latency, can i just do a
> > simple lock-break, via the patch below?
>
> with this patch the worst-case latency during NFS writeout is down to 40
> usecs (!).
>
> Lee: i've uploaded the -42-05 release with this patch included - could
> you test it on your (no doubt more complex than mine) NFS setup?

This fixes all the NFS related latency problems I was seeing. Now the
longest latency from an NFS kernel compile with "make -j64" is 391 usecs
in get_swap_page.

Lee