linux-kernel - Re: [PATCH 1/3] aoe: perform I/O completions in parallel

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Message-Id: <20130702144326.f891debce89e6b8f82efa39c@linux-foundation.org>
Date:	Tue, 2 Jul 2013 14:43:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ecashin@...erose.net
Cc:	linux-kernel@...r.kernel.org, ecashin@...aid.com
Subject: Re: [PATCH 1/3] aoe: perform I/O completions in parallel

On Tue, 2 Jul 2013 14:23:51 -0700 ecashin@...erose.net wrote:

> Some users have a large AoE target while others like to use
> many AoE targets at the same time.  In the latter case, there
> is an opportunity to greatly improve aggregate throughput by
> allowing different threads to complete the I/O associated
> with each target.  For 36 targets, 4 KiB read throughput
> roughly doubles, for example, with these changes in place.
> 
> ...
>
> --- a/drivers/block/aoe/aoecmd.c
> +++ b/drivers/block/aoe/aoecmd.c
> @@ -35,14 +35,24 @@ module_param(aoe_maxout, int, 0644);
>  MODULE_PARM_DESC(aoe_maxout,
>  	"Only aoe_maxout outstanding packets for every MAC on eX.Y.");
>  
> -static wait_queue_head_t ktiowq;
> -static struct ktstate kts;
> +/* The number of online cpus in the system,
> + * this dictates the number of ktio threads
> + * which will be spawned.
> + */
> +static int ncpus;

I can see that doing it this way simplifies the code rather a lot, but
of course CPU hotplug can and will make ncpus grossly different from
the current num_online_cpus.

I suggest it's worth adding a comment here mentioning this, and
explaining why and how that's OK.  If it indeed is OK ;)

Also, these patches were sent as being from ecashin@...erose.net.  I
rewrote that to ecashin@...aid.com which is what I suspect you
intended.  You can do this override yourself by putting a From: line
right at the top of the changelog.
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