linux-kernel - Re: [PATCH 5/5] virtio-blk: implement ->make

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Message-ID: <20111006135309.GA27941@kernel.dk>
Date:	Thu, 6 Oct 2011 15:53:09 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] virtio-blk: implement ->make_request

On Wed, Oct 05 2011, Christoph Hellwig wrote:
> Add an alternate I/O path that implements ->make_request for virtio-blk.
> This is required for high IOPs devices which get slowed down to 1/5th of
> the native speed by all the locking, memory allocation and other overhead
> in the request based I/O path.

We definitely have some performance fruit hanging rather low in that
path, but a factor 5 performance difference sounds insanely excessive. I
haven't looked at virtio_blk in detail, but I've done 500K+ IOPS on
request based drivers before (yes, on real hardware). So it could be
that virtio_blk is just doing things rather suboptimally in some places,
and that it would be possible to claim most of that speedup there too.

-- 
Jens Axboe

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