Messages in this thread Patch in this message | | | Subject | Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed | From | Corrado Zoccolo <> | Date | Wed, 9 Dec 2009 20:45:16 +0100 |
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On Wed, Dec 9, 2009 at 8:05 PM, Jens Axboe <jens.axboe@oracle.com> wrote: > On Wed, Dec 09 2009, Jeff Moyer wrote: >> OK. Can we put a comment in there and change the initialization to >> cfq_slice_sync * 10? > > Agree, that would be MUCH easier to understand. > Sure, we can put a comment there, but I don't like hardcoding a constant that depends on how the formula is computed (what if the formula is changed, and it doesn't depend on cfq_slice_sync any more, or if cfq_slice_sync changes dynamically?). When I wrote it, what I really meant was exactly what you read in the C code (assume the last delayed sync happened 1 second ago). Then, the effect would be to start with a queue depth of 10 with the current formula, but even if we change the formula, 1 second is still meaningful (while 10 *cfq_slice_sync, that has the same value, becomes misleading). So my proposed fix is just:
From f06cd83b45b3a7ee13ae7322197b610085dc70dd Mon Sep 17 00:00:00 2001 From: Corrado Zoccolo <corrado@localhost.(none)> Date: Wed, 9 Dec 2009 20:40:16 +0100 Subject: [PATCH] cfq-iosched: commenting non-obvious initialization
Added a comment to explain the initialization of last_delayed_sync.
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com> --- block/cfq-iosched.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 98b15b9..69ecee7 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3759,6 +3759,10 @@ static void *cfq_init_queue(struct request_queue *q) cfqd->cfq_latency = 1; cfqd->cfq_group_isolation = 0; cfqd->hw_tag = -1; + /* + * we optimistically start assuming sync ops weren't delayed in last + * second, in order to have larger depth for async operations. + */ cfqd->last_delayed_sync = jiffies - HZ; INIT_RCU_HEAD(&cfqd->rcu); return cfqd; -- 1.6.2.5
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