From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39536) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xwv40-0004mV-Iv for qemu-devel@nongnu.org; Fri, 05 Dec 2014 10:45:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xwv3r-00060e-8s for qemu-devel@nongnu.org; Fri, 05 Dec 2014 10:45:00 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58248) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xwv3q-0005zv-VX for qemu-devel@nongnu.org; Fri, 05 Dec 2014 10:44:51 -0500 Message-ID: <5481C9CB.70805@redhat.com> Date: Fri, 05 Dec 2014 08:05:47 -0700 From: Eric Blake MIME-Version: 1.0 References: <1417780229-6930-1-git-send-email-pl@kamp.de> <1417780229-6930-5-git-send-email-pl@kamp.de> In-Reply-To: <1417780229-6930-5-git-send-email-pl@kamp.de> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="mXnjsU9BbdxPQpi3Q6ur2FiNBBTMRqILF" Subject: Re: [Qemu-devel] [RFC PATCH V2 4/4] virtio-blk: introduce multiread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven , qemu-devel@nongnu.org Cc: kwolf@redhat.com, famz@redhat.com, benoit@irqsave.net, ming.lei@canonical.com, armbru@redhat.com, mreitz@redhat.com, stefanha@redhat.com, pbonzini@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --mXnjsU9BbdxPQpi3Q6ur2FiNBBTMRqILF Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 12/05/2014 04:50 AM, Peter Lieven wrote: > this patch finally introduce multiread support to virtio-blk while s/introduce/introduces/ s/virtio-blk while/virtio-blk. While/ > multiwrite support was there for a long time read support was missing. s/time/time,/ >=20 > To achieve this the patch does serveral things which might need futher s/serveral/several/ s/futher/further/ > explaination: s/explaination/explanation/ >=20 > - the whole merge and multireq logic is moved from block.c into > virtio-blk. This is move is a preparation for directly creating a > coroutine out of virtio-blk. Can this move be done as a separate prerequisite patch? Mixing code motion and new features in the same patch is harder to review. >=20 > - requests are only merged if they are strictly sequential and no s/sequential/sequential,/ > longer sorted. This simplification decreases overhead and reduces > latency. It will also merge some requests which were unmergable befo= re. >=20 > The old algorithm took up to 32 requests sorted them and tried to me= rge s/requests/requests,/ > them. The outcome was anything between 1 and 32 requests. In case of= > 32 requests there were 31 requests unnecessarily delayed. >=20 > On the other hand lets imagine e.g. 16 unmergeable requests followed= s/lets/let's/ > by 32 mergable requests. The latter 32 requests would have been spli= t > into two 16 byte requests. >=20 > Last the simplified logic allows for a fast path if we have only a > single request in the multirequest. In this case the request is sent= as > ordinary request without mulltireq callbacks. s/mulltireq/multireq/ >=20 > As a first benchmark I installed Ubuntu 14.04.1 on a ramdisk. The numbe= r of > merged requests is in the same order while the latency is slightly decr= eased. > One should not stick too much to the numbers because the number of wr_r= equests > are highly fluctuant. I hope the numbers show that this patch is at lea= st > not causing too big harm: >=20 I'll leave the actual patch review to developers more knowledgeable about block behavior. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --mXnjsU9BbdxPQpi3Q6ur2FiNBBTMRqILF Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg iQEcBAEBCAAGBQJUgcnLAAoJEKeha0olJ0NqcX8H/i5gxNP/P3SJDYii/BjbjjsR CbUIp9l25fODsHtMVMyxJ4JamcFxpmKmHQJcTN5zAKb614omUEvCHykT4iajSHiD n+BLnb4pQqCDplZmPeDx0+0chsWj6uCkPzKvwKk5uLe8GsQBZ27TTWwgyPV55Zhn 80OUdP+G3RD55xLbUG3Vn1We/ET6CounkeF9zVLTZ5eTlJExi5Q5iS9COYxS+EAC dnQ7PPemfvla5umIi3+a/ZHEE7KaCQngGhdtkl9NuEfBuyvEVU06tGImNXeYQolJ Qql8oyoswdU0Q2cYmTq1eokOYRKSH+TDpAv/TYJQDHForjkqw2Mfl+wpzgZNUPM= =AqMr -----END PGP SIGNATURE----- --mXnjsU9BbdxPQpi3Q6ur2FiNBBTMRqILF--