Messages in this thread Patch in this message | | | Date | Fri, 25 Dec 2009 17:10:30 +0800 | From | Shaohua Li <> | Subject | [RFC]cfq-iosched: quantum check tweak |
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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 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 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
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)) + return 1; + + return 0; +} + static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq) { unsigned int max_dispatch; @@ -2275,7 +2287,8 @@ static bool cfq_may_dispatch(struct cfq_ /* * We have other queues, don't allow more IO from this one */ - if (cfqd->busy_queues > 1) + if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq) + && cfqd->cfq_latency) return false; /*
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