From: Andrew Morton <akpm@linux-foundation.org>
To: sjayaraman@suse.de
Cc: Jens Axboe <axboe@kernel.dk>, LKML <linux-kernel@vger.kernel.org>,
Shaohua Li <shaohua.li@intel.com>,
Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH v2] block: document blk-plug
Date: Mon, 29 Aug 2011 14:48:43 -0700 [thread overview]
Message-ID: <20110829144843.c8e9d397.akpm@linux-foundation.org> (raw)
In-Reply-To: <4E5B77D5.7090006@suse.de>
On Mon, 29 Aug 2011 16:58:21 +0530
Suresh Jayaraman <sjayaraman@suse.de> wrote:
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -863,17 +863,23 @@ struct request_queue *blk_alloc_queue_node(gfp_t, int);
> extern void blk_put_queue(struct request_queue *);
>
> /*
> + * blk_plug allows to build up a queue of related requests by holding the I/O
> + * fragments for a short period. This allows merging of sequential requests
> + * into single larger request. As the requests are moved from per-task list to
> + * the device's request_queue in a batch, this results in improved
> + * scalability as the lock contention for request_queue lock is reduced.
> + *
> * Note: Code in between changing the blk_plug list/cb_list or element of such
> * lists is preemptable, but such code can't do sleep (or be very careful),
> * otherwise data is corrupted. For details, please check schedule() where
> * blk_schedule_flush_plug() is called.
What does the older part of this comment mean? If a code section is
preemptible then it *will* sleep. That's what preemption does.
next prev parent reply other threads:[~2011-08-29 21:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-29 11:28 [PATCH v2] block: document blk-plug Suresh Jayaraman
2011-08-29 21:48 ` Andrew Morton [this message]
2011-08-30 5:21 ` Suresh Jayaraman
2011-08-30 7:00 ` Shaohua Li
2011-09-05 12:46 ` Suresh Jayaraman
2011-09-06 0:55 ` Shaohua Li
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