linux-kernel - Re: [PATCH] cfq: get rid of cfqq hash

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Message-ID: <20070424122739.GJ3744@kernel.dk>
Date:	Tue, 24 Apr 2007 14:27:39 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Vasily Tarasov <vtaras@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, OVZDL <devel@...nvz.org>
Subject: Re: [PATCH] cfq: get rid of cfqq hash

On Tue, Apr 24 2007, Vasily Tarasov wrote:
> From: Vasily Tarasov <vtaras@...nvz.org>
> 
> cfq hash is no more necessary.  We always can get cfqq from io context.
> cfq_get_io_context_noalloc() function is introduced, because we don't want to
> allocate cic on merging and checking may_queue.
> In order to identify sync queue we've used hash key = CFQ_KEY_ASYNC. Since hash
> is eliminated we need to use other criterion: sync flag for queue is added.
> In all places where we dig in rb_tree we're in current context, so no
> additional locking is required.
> 
> 
> Advantages of this patch: no additional memory for hash, no seeking in hash,
> code is cleaner. But it is necessary now to seek cic in per-ioc rbtree, but
> it is faster:
> - most processes work only with few devices
> - most systems have only few block devices
> - it is a rb-tree

Vasily, thanks for doing this, it's a good cleanup. One request, though
- care to rebase this against the cfq devel branch? I'm afraid it's
nowhere near applying right now.

-- 
Jens Axboe

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