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: Thu, 24 Sep 2015 05:35:02 +0200 Message-ID: <1443065702.3276.15.camel@citrix.com> References: <55FFD3CD.3030004@citrix.com> <1442845472.2691.88.camel@citrix.com> <560134A002000078000A43AF@prv-mh.provo.novell.com> <56017B4102000078000A46CD@prv-mh.provo.novell.com> <56027478.1040604@citrix.com> <5602C470.4000609@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1358387171121440024==" 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 , Jan Beulich Cc: George Dunlap , Andrew Cooper , "Tian, Kevin" , Keir Fraser , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org --===============1358387171121440024== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-dQezUh3kGNUURG25shCv" --=-dQezUh3kGNUURG25shCv Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2015-09-24 at 01:50 +0000, Wu, Feng wrote: > > -----Original Message----- > > From: George Dunlap [mailto:george.dunlap@citrix.com] > > This seems to me to be a cleaner design. It removes the need to > > modify > > any code on context-switch path. It moves modification of NDST and > > most > > modifications of SN closer to where I think they logically go. It > > reduces the number of unnecessary PI interrupts delivered to the > > hypervisor (by suppressing notifications most of the time spend in > > the > > hypervisor), and automatically deals with the "spurious interrupts > > during tasklet execution / vcpu offline lazy context switch" issue > > we > > were talking about with the other thread. >=20 > One issue is the number of vmexits is far far bigger than the number > of > context switch. I test it for a quite short time and it shows there > are > 2910043 vmexits and 71733 context switch (only count the number in > __context_switch() since we only change the PI state in this > function). > If we change the PI state in each vmexit/vmentry, I am afraid this > will > hurt the performance. >=20 Interesting. Hard to tell without actually trying, though. Personally, I'd agree with George and Jan that the vmexit solution is more self contained, and hence preferable. I don't really dislike the __context_switch() solution, though, and I'd be fine to live with it, especially considering these numbers. I guess the absolute best would be for you to prototype both, and try gathering some performance numbers for comparison... Is this asking too much? :-) Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-dQezUh3kGNUURG25shCv 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 iEYEABECAAYFAlYDb2cACgkQk4XaBE3IOsQZjwCeOngbSGesnwYo0Hk5tPySAybg pA0Anj0enWvyqZqR9wZDUASuafcy0QuV =LGbR -----END PGP SIGNATURE----- --=-dQezUh3kGNUURG25shCv-- --===============1358387171121440024== 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 --===============1358387171121440024==--