From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gregory Haskins Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33 Date: Mon, 21 Dec 2009 11:46:13 -0500 Message-ID: <4B2FA655.6030205@gmail.com> References: <4B1D4F29.8020309@gmail.com> <20091218215107.GA14946@elte.hu> <4B2F9582.5000002@gmail.com> <4B2F978D.7010602@redhat.com> <4B2F9C85.7070202@gmail.com> <4B2FA42F.3070408@codemonkey.ws> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigF6EF3FBD5F225B60CBED56A8" Cc: Avi Kivity , Ingo Molnar , kvm@vger.kernel.org, Andrew Morton , torvalds@linux-foundation.org, "linux-kernel@vger.kernel.org" , netdev@vger.kernel.org, "alacrityvm-devel@lists.sourceforge.net" To: Anthony Liguori Return-path: In-Reply-To: <4B2FA42F.3070408@codemonkey.ws> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigF6EF3FBD5F225B60CBED56A8 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 12/21/09 11:37 AM, Anthony Liguori wrote: > On 12/21/2009 10:04 AM, Gregory Haskins wrote: >> No, B and C definitely are, but A is lacking. And the performance >> suffers as a result in my testing (vhost-net still throws a ton of exi= ts >> as its limited by virtio-pci and only adds about 1Gb/s to virtio-u, fa= r >> behind venet even with things like zero-copy turned off). >> =20 >=20 > How does virtio-pci limit vhost-net? The only time exits should occur > are when the guest notifies the host that something has been placed on > the ring. Since vhost-net has no tx mitigation scheme right now, the > result may be that it's taking an io exit on every single packet but > this is orthogonal to virtio-pci. >=20 > Since virtio-pci supports MSI-X, there should be no IO exits on > host->guest notification other than EOI in the virtual APIC. The very best you can hope to achieve is 1:1 EOI per signal (though today virtio-pci is even worse than that). As I indicated above, I can eliminate more than 50% of even the EOIs in trivial examples, and even more as we scale up the number of devices or the IO load (or both). > This is a > light weight exit today and will likely disappear entirely with newer > hardware. By that argument, this is all moot. New hardware will likely obsolete the need for venet or virtio-net anyway. The goal of my work is to provide an easy to use framework for maximizing the IO transport _in lieu_ of hardware acceleration. Software will always be leading here, so we don't want to get into a pattern of waiting for new hardware to cover poor software engineering. Its simply not necessary in most cases. A little smart software design and a framework that allows it to be easily exploited/reused is the best step forward, IMO. Kind Regards, -Greg --------------enigF6EF3FBD5F225B60CBED56A8 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.11 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAksvplUACgkQP5K2CMvXmqEr4gCcD77IW07qp4uZvo3sFrMNKxgp KKcAoIPUd2xPt5G57TydRznBMp5v4PWd =mOYF -----END PGP SIGNATURE----- --------------enigF6EF3FBD5F225B60CBED56A8--