> On Wed, Apr 07 2010, Jeff Moyer wrote:
> > Hi again,
> >
> > So, here's another stab at fixing this. This patch is very much an RFC,
> > so do not pull it into anything bound for Linus. ;-) For those new to
> > this topic, here is the original posting:
http://lkml.org/lkml/2010/4/1/344
> >
> > The basic problem is that, when running iozone on smallish files (up to
> > 8MB in size) and including fsync in the timings, deadline outperforms
> > CFQ by a factor of about 5 for 64KB files, and by about 10% for 8MB
> > files. From examining the blktrace data, it appears that iozone will
> > issue an fsync() call, and will have to wait until it's CFQ timeslice
> > has expired before the journal thread can run to actually commit data to
> > disk.
> >
> > The approach below puts an explicit call into the filesystem-specific
> > fsync code to yield the disk so that the jbd[2] process has a chance to
> > issue I/O. This bring performance of CFQ in line with deadline.
> >
> > There is one outstanding issue with the patch that Vivek pointed out.
> > Basically, this could starve out the sync-noidle workload if there is a
> > lot of fsync-ing going on. I'll address that in a follow-on patch. For
> > now, I wanted to get the idea out there for others to comment on.
> >
> > Thanks a ton to Vivek for spotting the problem with the initial
> > approach, and for his continued review.
>
> I like the concept, it's definitely useful (and your results amply
> demonstrate that). I was thinking if there was a way in through the ioc
> itself, rather than bdi -> queue and like you are doing. But I can't
> think of a nice way to do it, so this is probably as good as it gets.
>
