Re: [patch,rfc v2] ext3/4: enhance fsync performance when using cfq

[Jeff Moyer <jmoyer@redhat.com>]

Vivek Goyal <vgoyal@redhat.com> writes:

> On Thu, Apr 08, 2010 at 10:03:24AM -0400, Jeff Moyer wrote:
>> Which actually brings up the question of whether this needs some
>> knowledge of whether the journal is on the same device as the file
>> system!  In such a case, we need not yield.  I think I'll stick my head
>> in the sand for this one.  ;-)
>
> Jeff even if journal is not on same device, what harm yielding could do?
> Anyway there is no IO on that queue and we are idling. Only side affect is
> that yielding process could lose a bit if after fsync it immediately submits
> more IO. Because this process has yielded it slice, it is back in the queue
> instead of doing more IO in the current slice immediately.

What happens if the journal is on a super fast device, and finishes up
very quickly allowing our process to initiate more I/O within the idle
window?

Cheers,
Jeff