Messages in this thread | | | Date | Fri, 25 Dec 2009 10:44:40 +0100 | Subject | Re: [RFC]cfq-iosched: quantum check tweak | From | Corrado Zoccolo <> |
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On Fri, Dec 25, 2009 at 10:10 AM, Shaohua Li <shaohua.li@intel.com> wrote: > Currently a queue can only dispatch up to 4 requests if there are other queues. > This isn't optimal, device can handle more requests, for example, AHCI can > handle 31 requests. I can understand the limit is for fairness, but we could > do some tweaks: > 1. if the queue still has a lot of slice left, sounds we could ignore the limit ok. You can even scale the limit proportionally to the remaining slice (see below).
> 2. we could keep the check only when cfq_latency is on. For uses who don't care > about latency should be happy to have device fully piped on. I wouldn't overload low_latency with this meaning. You can obtain the same by setting the quantum to 32. > > I have a test of random direct io of two threads, each has 32 requests one time > without patch: 78m/s > with tweak 1: 138m/s > with two tweaks and disable latency: 156m/s
Please, test also with competing seq/random(depth1)/async workloads, and measure also introduced latencies.
> > Signed-off-by: Shaohua Li <shaohua.li@intel.com> > --- > block/cfq-iosched.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > Index: linux-2.6/block/cfq-iosched.c > =================================================================== > --- linux-2.6.orig/block/cfq-iosched.c > +++ linux-2.6/block/cfq-iosched.c > @@ -2242,6 +2242,18 @@ static int cfq_forced_dispatch(struct cf > return dispatched; > } > > +static inline bool cfq_slice_used_soon(struct cfq_data *cfqd, > + struct cfq_queue *cfqq) > +{ > + /* the queue hasn't finished any request, can't estimate */ > + if (cfq_cfqq_slice_new(cfqq)) > + return 1; > + if (time_after(jiffies + cfqd->cfq_slice_idle, cfqq->slice_end)) here I would use jiffies + cfqd->cfq_slice_idle * (cfqq->queued[0] + cfqq->queued[1]) to obtain the proper scaling > + return 1; > + > + return 0; > +} > + > static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq) > { > unsigned int max_dispatch;
Thanks, Corrado
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dott. Corrado Zoccolo mailto:czoccolo@gmail.com PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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