From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] MMIO: Make coalesced mmio use a device per zone Date: Tue, 19 Jul 2011 22:00:25 +0200 Message-ID: <4E25E259.1080302@web.de> References: <1311063011-4430-1-git-send-email-levinsasha928@gmail.com> <4E2544F3.9030203@redhat.com> <1311069182.9174.1.camel@lappy> <4E255584.1030003@redhat.com> <1311070673.9174.4.camel@lappy> <4E255D44.8000107@redhat.com> <4E25BB6B.90907@siemens.com> <4E25BC46.1040200@redhat.com> <4E25BD8D.1030509@siemens.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigC130488A73FDFC26609E784E" Cc: Avi Kivity , "kvm@vger.kernel.org" , Marcelo Tosatti To: Sasha Levin Return-path: Received: from fmmailgate02.web.de ([217.72.192.227]:38301 "EHLO fmmailgate02.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750957Ab1GSUA1 (ORCPT ); Tue, 19 Jul 2011 16:00:27 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigC130488A73FDFC26609E784E Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2011-07-19 21:28, Sasha Levin wrote: > On Tue, Jul 19, 2011 at 8:23 PM, Jan Kiszka wr= ote: >> On 2011-07-19 19:17, Avi Kivity wrote: >>> On 07/19/2011 08:14 PM, Jan Kiszka wrote: >>>> >>>> Another improvement - unfortunately less transparent for user space = - >>>> would be to overcome the single ring buffer that forces us to hold a= >>>> central lock in user space while processing the entries. We rather n= eed >>>> per-device rings. While waiting for coalesced VGA MMIO being process= ed, >>>> way too many kittens are killed. >>>> >>>> I have this on our agenda, but I wouldn't be disappointed as well if= >>>> someone else is faster. >>> >>> The socket mmio would have accomplished this as well. >=20 > It's possible to process the coalesced mmio ring without waiting for > an exit, no? Is the performance that bad? You do not necessarily have to wait for an exit, but you obviously have to synchronize all readers, including vcpus issuing some serializing access. By the time you have >1 and VGA or other heavy users are among them, the rest suffers from increased latencies (you easily get beyond hundreds of ms if graphic is involved). That might be ok for ordinary workload, but it's unacceptable for real-time guests. >=20 > I would have thought it's reasonable after seeing how well > virtio-blk/virtio-net behave. >=20 >> >> I haven't followed the outcome in all details - is that approach dead >> due to its complexity? >=20 > The ability to allow reverse direction in the socket ('read' support > instead of just write) is making it a bit complex. Hopefully it'll be > ready soon. Great, will have an eye on it and take care of the QEMU integration - unless you would like to do that as well... :) Jan --------------enigC130488A73FDFC26609E784E Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk4l4lkACgkQitSsb3rl5xRRzACdFPZz2m7khk02IRJtRQGP3lVQ VZEAn1x/ndXA7IJx0n5WXPfuqNB4Wwuj =01qU -----END PGP SIGNATURE----- --------------enigC130488A73FDFC26609E784E--