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Message-ID: <20110308205422.GI27455@redhat.com>
Date: Tue, 8 Mar 2011 15:54:22 -0500
From: Vivek Goyal <vgoyal@...hat.com>
To: lina <lulina_nuaa@...mail.com>
Cc: linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: blk-throttle.c : When limit is changed, must start a new slice
On Tue, Mar 08, 2011 at 11:03:59PM +0800, lina wrote:
[..]
> >> Unfortunately, the following patch still has 5~10 seconds latency. I have no
> >> idea to resolve this problem, it seens hard to find a more suitable func to
> >> call throtl_start_new_slice().
> >
> >So are you saying that following patch did not solve the latnecy issue?
> >Resetting slice upon limit change did not work for you?
> ></:includetail>
> </:includetail>
> Yes, the following patch did not solve the latency issue. There is still 5~10</:includetail>
> seconds latency when I change the limit from a very high value to low. From </:includetail>
> blktrace, I find that the throtl_process_limit_change() is called after work </:includetail>
> queue </:includetail>delay.</:includetail>
> </:includetail>
> Thanks</:includetail>
> Lina</:includetail>
> </:includetail></:includetail>
> </:includetail>>Thanks
Ok,
Can you try the attached patch. I think what was happening that after
changing limits, work was not being scheduled as there were no queued
bios hence no slice reset was taking place immediately.
Also I am not sure from where these "</:includetail>" strings are coming.
Looks like your mailer is inserting those. Trying sending mails in text
format.
Thanks
Vivek
---
block/blk-throttle.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
Index: linux-2.6/block/blk-throttle.c
===================================================================
--- linux-2.6.orig/block/blk-throttle.c 2011-03-04 13:59:45.000000000 -0500
+++ linux-2.6/block/blk-throttle.c 2011-03-08 15:41:19.384654732 -0500
@@ -757,6 +757,14 @@ static void throtl_process_limit_change(
" riops=%u wiops=%u", tg->bps[READ],
tg->bps[WRITE], tg->iops[READ],
tg->iops[WRITE]);
+ /*
+ * Restart the slices for both READ and WRITES. It
+ * might happen that a group's limit are dropped
+ * suddenly and we don't want to account recently
+ * dispatched IO with new low rate
+ */
+ throtl_start_new_slice(td, tg, 0);
+ throtl_start_new_slice(td, tg, 1);
tg_update_disptime(td, tg);
tg->limits_changed = false;
}
@@ -825,7 +833,8 @@ throtl_schedule_delayed_work(struct thro
struct delayed_work *dwork = &td->throtl_work;
- if (total_nr_queued(td) > 0) {
+ /* schedule work if limits changed even if no bio is queued */
+ if (total_nr_queued(td) > 0 || atomic_read(&td->limits_changed)) {
/*
* We might have a work scheduled to be executed in future.
* Cancel that and schedule a new one.
@@ -1023,6 +1032,19 @@ int blk_throtl_bio(struct request_queue
/* Bio is with-in rate limit of group */
if (tg_may_dispatch(td, tg, bio, NULL)) {
throtl_charge_bio(tg, bio);
+
+ /*
+ * We need to trim slice even when bios are not being queued
+ * otherwise it might happen that a bio is not queued for
+ * a long time and slice keeps on extending and trim is not
+ * called for a long time. Now if limits are reduced suddenly
+ * we take into account all the IO dispatched so far at new
+ * low rate and * newly queued IO gets a really long dispatch
+ * time.
+ *
+ * So keep on trimming slice even if bio is not queued.
+ */
+ throtl_trim_slice(td, tg, rw);
goto out;
}
--
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