From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: [PATCH v7 15/17] vmx: VT-d posted-interrupt core logic handling Date: Wed, 23 Sep 2015 09:59:50 +0200 Message-ID: <1442995190.24964.2.camel@citrix.com> References: <55FFCB67.3050900@citrix.com> <1442842304.2691.67.camel@citrix.com> <1442844706.2691.79.camel@citrix.com> <560130BD.6090700@citrix.com> <56013185.4070200@citrix.com> <1442929201.2691.97.camel@citrix.com> <5601628B.2090209@citrix.com> <1442932719.2691.109.camel@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1568973175825449975==" Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "Wu, Feng" , George Dunlap Cc: "Tian, Kevin" , Keir Fraser , George Dunlap , Andrew Cooper , "xen-devel@lists.xen.org" , Jan Beulich List-Id: xen-devel@lists.xenproject.org --===============1568973175825449975== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-Kpn6zDstNPi9UGAItuzM" --=-Kpn6zDstNPi9UGAItuzM Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2015-09-23 at 05:52 +0000, Wu, Feng wrote: > George & Dario, thanks much for sharing so many scheduler knowledge > to me, it is very useful.=20 > Well, we're lucky enough that it's our job to do that. :-D > > > So the only downside to doing everything in block(), wake(), and > > > __context_switch() is that if a VM is offline, or preempted by a > > > tasklet, and an interrupt comes in, we will get a spurious PI > > > (i.e., > > > one > > > which interrupts us but we can't do anything useful about). > > >=20 > > Indeed. And that also seems bearable to me. Feng, are there reasons > > why > > you think it's not? >=20 > I cannot think the bad effect of the spurious PI as well. I was just > a little > confused about we can do this and why we don't do this. Maybe > context_switch() is a critical path, if we can bear those spurious > PI, > it is not worth adding those logic in it at the cost of some > performance > lost during scheduling. Is this your concern? >=20 The, however small, performance implications of even only checking whether the hooks should be invoked is certainly good to be avoided, especially, on non-PI enabled (and even more so on non-VMX) hardware. However, what I think it is more important in this case, is that not having the hooks in context_switch() yields a better results from an architectural and code organization point of view. It makes both the context switch code, and the PI code, easier to understand and to maintain. So, thanks to you and Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-Kpn6zDstNPi9UGAItuzM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEABECAAYFAlYCW/YACgkQk4XaBE3IOsRRSQCff/mPPfGN5b8pkAuB/RGK6hUi 7nEAn3NBbac+Nj2yBaepOgMP450IUIF9 =lvf2 -----END PGP SIGNATURE----- --=-Kpn6zDstNPi9UGAItuzM-- --===============1568973175825449975== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel --===============1568973175825449975==--