linux-kernel - Re: CFQ: async queue blocks the whole system

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Date:	Fri, 10 Jun 2011 05:20:31 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tao Ma <tm@....ma>
Cc:	Shaohua Li <shaohua.li@...el.com>, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: CFQ: async queue blocks the whole system

On Fri, Jun 10, 2011 at 11:02:11AM +0800, Tao Ma wrote:

[..]
> > I don't think we can give a deadline for async request, because we
> > still want to give sync high priority. We can give async some slices,
> > so for a workload of small number of async requests and large number
> > sync requests, we don't starve async too much. But for a workload with
> > large number of sync/async requests, async will be starved for sure
> > and we can't solve this in cfq.
> OK, so if you guys thinks a 500 seconds wait is good for an async write
> to complete, fine, then we have to switch to deadline.

I don't think that starving WRITES completely is a good idea. Especially
given the fact that you were not able to dispatch WRITES for 500 seconds.
This needs fixing.

Its not about giving hard deadline to WRITES, but making sure we don't
starve them completely and they also make some progress.

Thanks
Vivek
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