linux-kernel - Re: [PATCH 2/9] block: Stop abusing rq->csd.list in blk-softirq

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Date:	Thu, 30 Jan 2014 23:12:41 +0100
From:	Jan Kara <jack@...e.cz>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	pmladek@...e.cz, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9] block: Stop abusing rq->csd.list in blk-softirq

On Thu 30-01-14 18:01:20, Frederic Weisbecker wrote:
> On Thu, Jan 30, 2014 at 04:45:23PM +0100, Jan Kara wrote:
> >   Hi,
> > 
> > On Thu 30-01-14 13:39:18, Frederic Weisbecker wrote:
> > > I'm currently working on some cleanups on IPI code too and working on top
> > > of these patches, just have a few comments:
> >   Great, thanks!
> > 
> > > On Mon, Dec 23, 2013 at 09:39:23PM +0100, Jan Kara wrote:
> > > > Abusing rq->csd.list for a list of requests to complete is rather ugly.
> > > > Especially since using queuelist should be safe and much cleaner.
> > > 
> > > It would be nice to have a few more details that explain why doing so is safe
> > > wrt a block request lifecycle. At least something that tells why rq->queuelist
> > > can't be ever used concurrently by the time we send the IPI and we trigger/raise
> > > the softirq.
> >   Sure. Should I send the patch to you with an updated changelog and added
> > comment you requested?
> 
> Yeah that would be nice!
  OK, the updated patch is attached.

> For more precision, I would like to apply these:
> 
> 1) block: Stop abusing csd.list for fifo_time
> 2) block: Stop abusing rq->csd.list in blk-softirq
> 3) kernel: use lockless list for smp_call_function_single()
> 4) smp: Teach __smp_call_function_single() to check for offline cpus
> 
> This is because I need to tweak a bit the IPI code for some nohz
> functionnality. I'm not sure about the result but in any case these
> llist based cleanups look very nice, so lets try to push them. I'm also
> working on some consolidation between __smp_call_function_single()
> and smp_call_function_single() since they share almost the same code.
> 
> Also this shouldn't conflict with Andrew's tree if he applies these as well
> since -mm is based on -next. And the printk part should still go through his
> tree I think.
  Sure, that should be no problem. Jens might have the patch somewhere in
the linux-block.git but any conflict should be easy to resolve.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR

View attachment "0001-block-Stop-abusing-rq-csd.list-in-blk-softirq.patch" of type "text/x-patch" (2298 bytes)