linux-kernel - Re: Re: [PATCH] blkcg: Before starting a new slice, firstly count bps/iops limit in func tg_may

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Date:	Tue, 15 Jan 2013 08:30:22 +0800
From:	majianpeng <majianpeng@...il.com>
To:	"Vivek Goyal" <vgoyal@...hat.com>
Cc:	axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>, tj <tj@...nel.org>
Subject: Re: Re: [PATCH] blkcg: Before starting a new slice, firstly count bps/iops limit in func tg_may_dispatch.

>On Mon, Jan 14, 2013 at 10:15:58AM +0800, majianpeng wrote:
>
>[..]
>> >Index: linux-2.6/block/blk-throttle.c
>> >===================================================================
>> >--- linux-2.6.orig/block/blk-throttle.c	2012-10-18 01:52:28.000000000 -0400
>> >+++ linux-2.6/block/blk-throttle.c	2013-01-14 03:40:41.355731375 -0500
>> >@@ -648,8 +648,14 @@ static bool tg_may_dispatch(struct throt
>> > 	 * If previous slice expired, start a new one otherwise renew/extend
>> > 	 * existing slice to make sure it is at least throtl_slice interval
>> > 	 * long since now.
>> >+	 *
>> >+	 * Start a new slice only if there is no bio queued in that direction.
>> >+	 * That bio is waiting to be dispatched and slice needs to be
>> >+	 * extended. It might happen that bio waited to be dispatched but
>> >+	 * workqueue execution got little late it might restart a new slice
>> >+	 * instead of taking all the waited time into account.
>> > 	 */
>> >-	if (throtl_slice_used(td, tg, rw))
>> >+	if (throtl_slice_used(td, tg, rw) && !tg->nr_queued[rw])
>> > 		throtl_start_new_slice(td, tg, rw);
>> > 	else {
>> > 		if (time_before(tg->slice_end[rw], jiffies + throtl_slice))
>> Hi vivek,
>> 	Your patch is ok.But i had a question:
>> What's condition tg->nr_queued[rw] = 0, but bio is not null?
>
>When a new bio is about to be queued in an empty group (look at
>blk_throtl_bio). At that time, tg->nr_queued[rw] might be 0 if no other
>bio is already queued.
>
>Thanks
>Vivek
I see. Thanks your time!

Jianpeng
Thanks!