linux-kernel - Re: [PATCH 4/4] blkio: Recalculate the throttled bio dispatch time upon throttle limit change

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Message-Id: <20100928101641.a2791513.randy.dunlap@oracle.com>
Date:	Tue, 28 Sep 2010 10:16:41 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH 4/4] blkio: Recalculate the throttled bio dispatch time
 upon throttle limit change

On Tue, 28 Sep 2010 13:10:59 -0400 Vivek Goyal wrote:

> o Currently any cgroup throttle limit changes are processed asynchronousy and
>   the change does not take affect till a new bio is dispatched from same group.
> 
> o It might happen that a user sets a redicuously low limit on throttling.
>   Say 1 bytes per second on reads. In such cases simple operations like mount
>   a disk can wait for a very long time.
> 
> o Once bio is throttled, there is no easy way to come out of that wait even if
>   user increases the read limit later.
> 
> o This patch fixes it. Now if a user changes the cgroup limits, we recalculate
>   the bio dispatch time according to new limits.
> 
> o Can't take queueu lock under blkcg_lock, hence after the change I wake
>   up the dispatch thread again which recalculates the time. So there are some
>   variables being synchronized across two threads without lock and I had to
>   make use of barriers. Hoping I have used barriers correctly. Any review of
>   memory barrier code especially will help.


Hi,
Has this report been addressed/fixed?


on i386:

blk-throttle.c:(.text+0x1abb8): undefined reference to `__udivdi3'
blk-throttle.c:(.text+0x1b1dc): undefined reference to `__udivdi3'


on linux-next 2010-0924 and 2010-0927.

---
~Randy
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