linux-kernel - Re: [PATCH] blk-mq: use __smp_call_function

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Message-ID: <20140109183507.GA23826@infradead.org>
Date:	Thu, 9 Jan 2014 10:35:07 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: use __smp_call_function_single directly

On Wed, Jan 08, 2014 at 02:31:15PM -0700, Jens Axboe wrote:
> On 01/08/2014 10:33 AM, Christoph Hellwig wrote:
> > __smp_call_function_single already avoids multiple IPIs by internally
> > queing up the items, and now also is available for non-SMP builds as
> > a trivially correct stub, so there is no need to wrap it.  If the
> > additional lock roundtrip cause problems my patch to convert the
> > generic IPI code to llists is waiting to get merged will fix it.
> 
> Thanks Christoph, applied it.

Btw, the same should be done to the null_blk ipi completion
path in theory.  But given that it always tries to IPI the local
CPU __smp_call_function_single turns into a simple indirect function
call, so I don't really understand the point of that code path at all.
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