linux-kernel - Re: [patch 1/3] raid5: offload stripe handle to workqueue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 1 Aug 2013 10:01:01 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
	neilb@...e.de, djbw@...com
Subject: Re: [patch 1/3] raid5: offload stripe handle to workqueue

On Wed, Jul 31, 2013 at 06:33:32AM -0400, Tejun Heo wrote:
> Hello,
> 
> On Wed, Jul 31, 2013 at 09:24:34AM +0800, Shaohua Li wrote:
> > stripe is the work unit actually. As I said, if I queue a work for each stripe,
> > just queue_work() will make the system blast because of the pwq->pool->lock
> > contention. dispatching one work has another side effect that I can't add block
> 
> Hmmm.... I see.  I'm not familiar with the code base and could be
> missing something but how does the custom stripe dispatch queue
> synchronize?  Doesn't that make use of a lock anyway?  If so, how
> would scheduling separate work items be worse?  

It does have lock, but when a stripe is queued to handle, no lock is required.
So the workqueue lock will be high contended.

> Also, can you please
> elaborate the block plug part?

Basically I do:

blk_start_plug()
handle_stripe() //may dispatch request
blk_end_plug()

If only handle one stripe between block plug, the plug is useless, so I need
handle several stripes.

Thanks,
Shaohua
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/