From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [GIT PULL] KVM fixes for 3.5-rc6 Date: Sat, 14 Jul 2012 09:00:01 +0200 Message-ID: <500118F1.8060300@web.de> References: <4FFEBB39.8090308@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig7FF571E121A0C3197AB0C4D5" Cc: Linus Torvalds , Avi Kivity , linux-kernel , Marcelo Tosatti , KVM list To: Thomas Gleixner Return-path: Received: from mout.web.de ([212.227.15.4]:55440 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753329Ab2GNHAj (ORCPT ); Sat, 14 Jul 2012 03:00:39 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig7FF571E121A0C3197AB0C4D5 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2012-07-14 04:25, Thomas Gleixner wrote: > On Fri, 13 Jul 2012, Thomas Gleixner wrote: >> On Fri, 13 Jul 2012, Linus Torvalds wrote: >>> On Fri, Jul 13, 2012 at 8:45 AM, Linus Torvalds >>> wrote: >>> At the same time, I do wonder if maybe MSI + IRQF_ONESHOT couldn't be= >>> improved. The fact that the KVM people think that the extra overhead >>> of IRQF_ONESHOT is a bad thing for MSI interrupts makes me wonder if >>> maybe this wouldn't be an area the irq layer couldn't be improved on.= >>> Maybe the MSI+IRQF_ONESHOT case could be improved. Because MSI is kin= d >>> of fundamentally one-shot, since it's a message-based irq scheme. So= >>> maybe the extra overhead is unnecessary in general, not just in this >>> particular KVM case. Hmm? >>> >>> Thomas, see the commentary of a76beb14123a ("KVM: Fix device >>> assignment threaded irq handler"). >> >> Groan. >> >> We already discussed to let the irq chip (in this case MSI) tell the >> core that it does not need the extra oneshot handling. That way the >> code which requests an threaded irq with the NULL primary handler >> works on both MSI and normal interrupts. >=20 > That's the kind of stuff which makes me go berserk, and just for the > record: the most complaints I get for going berserk are coming from > the virt folks. >=20 > I really can't understand why the virt folks think they are > special and do not have to talk to core maintainers. >=20 > Back then when I was doing the big irq cleanup, virt crap stood out by > far with the most idiotic^Wcreative "workarounds". Of course nobody > complained about me being moronic enough to come up with generic > solutions for their problems. >=20 > Though especially that commit including its changelog proves once > again the ignorance and desinterest of the virt crowd in solving > problems which are not only relevant to themself. >=20 > I whish you'd just refused to pull that nonsense and instead made them > talk to those folks who had a proper solution in mind already. >=20 > In fact we could have solved that proper weeks ago, if only people > would have raised the issue. June 1: http://thread.gmane.org/gmane.linux.kernel/1306742 The proper solution for us will be conditional direct IRQ delivery anyway [1], but those patches were not considered ready for 3.5. This patch here is a workaround to unbreak devices assignment in 3.5 after the IRQ layer changes without regressing noticeable /wrt overhead. Jan [1] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/92249 --------------enig7FF571E121A0C3197AB0C4D5 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/ iEYEARECAAYFAlABGRAACgkQitSsb3rl5xQ4cQCeOY0xLZzqwx3AZCELHi/EH61f PWEAoNg6/bOF+UZJhN+GjcwQYL0c2reB =mf8A -----END PGP SIGNATURE----- --------------enig7FF571E121A0C3197AB0C4D5--