From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: assign-dev: Purpose of interrupt_work Date: Mon, 12 Oct 2009 11:07:28 +0200 Message-ID: <4AD2F1D0.4090005@web.de> References: <4AD2D4B6.7030203@web.de> <20091012071310.GT16702@redhat.com> <4AD2DA57.6030006@web.de> <20091012074513.GV16702@redhat.com> <4AD2DFE2.4050406@web.de> <4AD2EB2D.5080909@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig4F00FB18F69E7A72CCC2D497" Cc: Gleb Natapov , kvm-devel To: Avi Kivity Return-path: Received: from fmmailgate03.web.de ([217.72.192.234]:46529 "EHLO fmmailgate03.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755179AbZJLJJ3 (ORCPT ); Mon, 12 Oct 2009 05:09:29 -0400 In-Reply-To: <4AD2EB2D.5080909@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig4F00FB18F69E7A72CCC2D497 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Avi Kivity wrote: > On 10/12/2009 09:50 AM, Jan Kiszka wrote: >>> Apic is lockless. For ioapic/pic I used spinlocks initially, but Avi >>> prefers mutexes. Theoretically it is possible to make them lockless, >>> but code will be complex and eventually more slow, since more then tw= o >>> atomic operation will be used on irq injection path. >>> =20 >> Well, lockless is another thing. >> >> But also converting to spinlocks would indeed add some overhead: >> irqsave/restore. But I wonder if this isn't worth it, at least when >> looking at the (supposed to be fast) device passthrough scenario which= >> would be simpler and faster. >> =20 >=20 > I'm worried about disabling irqs for non-device-assignment cases. It > would be more palatable if ioapic was completely O(1) (there are some > per-vcpu loops in there, shouldn't be too bad for 16 vcpus, but we want= > to scale). Yeah, what a pity. That's likely not solvable in a generic way, given that the guest finally decided how many VCPUs may listen to a line. OK, but dropping interrupt_work from the MSI path is still worthwhile, and probably more future-proof anyway. Jan --------------enig4F00FB18F69E7A72CCC2D497 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkrS8dAACgkQitSsb3rl5xQzegCgz+n64w0dzwFFuFvv2cSNbpGL FaUAoMNQ1DdMsxZsZNHCH/urpaKJyiIn =h/4p -----END PGP SIGNATURE----- --------------enig4F00FB18F69E7A72CCC2D497--