Re: [RFC][PATCH 1/3] sched, block: Move unplug

From: Vivek Goyal
Date: Wed Jun 22 2011 - 11:09:17 EST

On Wed, Jun 22, 2011 at 04:38:01PM +0200, Peter Zijlstra wrote:
> On Wed, 2011-06-22 at 16:30 +0200, Thomas Gleixner wrote:
> > > It is supposedly a real problem, not just an inkling. It's not about
> > > recursing indefinitely, the plug is fairly bounded. But the IO dispatch
> > > path can be pretty deep, and if you hit that deep inside the reclaim or
> > > file system write path, then you get dangerously close. Dave Chinner
> > > posted some numbers in the 2.6.39-rc1 time frame showing how close we
> > > got.
> >
> > Fair enough.
> > Ok. So we move it out and keep the from_scheduler flag so that code
> > does not go down the IO path from there.
> Won't punting the plug to a worker thread wreck all kinds of io
> accounting due to the wrong task doing the actual io submission?

I think all the accounting will the done in IO submission path and
while IO is added to plug. This is just plug flush so should not
have effect on accounting.

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