Re: 2.6.20-rc2+: CFQ halving disk throughput.

[Mark Lord]

Jens Axboe wrote:
> On Tue, Jan 02 2007, Jens Axboe wrote:
> > On Tue, Jan 02 2007, Rene Herman wrote:
> > > Jens Axboe wrote:
> > >
> > > > On Mon, Jan 01 2007, Andrew Morton wrote:
> > > > > The patch would appear to need this fix:
> > > > >
> > > > > --- a/block/cfq-iosched.c~a
> > > > > +++ a/block/cfq-iosched.c
> > > > > @@ -592,7 +592,7 @@ static int cfq_allow_merge(request_queue
> > > > > 	if (cfqq == RQ_CFQQ(rq))
> > > > > 		return 1;
> > > > >
> > > > > -	return 1;
> > > > > +	return 0;
> > > > > }
> > > > >
> > > > > static inline void
> > > > > _
> > > > >
> > > > > But that might not fix things...
> > > > Yeah it is, but I don't think it'll fix it (if anything, it'll be more
> > > > conservative).
> > > (to possibly save others from trying -- no, doesn't fix any)
> > As expected. The issue is rq_is_sync(rq) takes the data direction into
> > account as well, while bio_sync() only checks the sync bit. This should
> > fix it.
>
> And here a little more relaxed version, as Mark Lord suggested. We allow
> merge of async bio into a sync request, but not vice versa.
>
> Both patches pending testing, will do so now.

Performance is right back where it should be now, thanks!

I did have to massage the second patch to get it to apply cleanly
after the first patch.  You may want to regenerate it against -rc3.

Cheers
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