From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: Questions about the use of idle_vcpu[] Date: Mon, 18 Jan 2016 13:47:29 +0100 Message-ID: <1453121249.11427.83.camel@citrix.com> References: <569845B7.2060207@seas.upenn.edu> <1453114800.11427.78.camel@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============6174849530811643507==" 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: George Dunlap Cc: Tianyang Chen , Meng Xu , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org --===============6174849530811643507== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-eDutoBco3j8p+a60x/U/" --=-eDutoBco3j8p+a60x/U/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2016-01-18 at 12:37 +0000, George Dunlap wrote: > On Mon, Jan 18, 2016 at 11:00 AM, Dario Faggioli > wrote: > > >=C2=A0 > > Credit2, AFAICR, could also avoid _always_ re-setting the timer, > > but it > > does need to do that at least a few times, even when idle is > > selected, > > because of the dynamic load tracking mechanism it includes. In > > fact, > > that is based on a 'decaying average', which in turns relies on > > csched2_schedule() to run and update the statistics, even when the > > cpu > > is idle. If we don't do that, the load tracking mechanism will > > never > > see that the cpu (well, it's actually the runqueue) is idle, and > > the > > load will never go down! :-/ >=20 > I don't think that's true -- it looks like balance_load() will call > __update_runq_load() on the "other" runqueue before considering it, > and will also call __update_svc_load() on each vcpu before > considering > it.=C2=A0=C2=A0Shouldn't that suffice? >=20 Mm... It looks like it should. And yet, I observed that 'load not going down' behavior while doing development for the patch I mentioned, both on Credit2 and Credit (with patches for extending the load tracking to Credit applied). I was, in the same series, also trying to optimize the Credit2's load balancer a little bit, though, so what I saw may be the effect of some other change of mine... I'll have a go at just disabling the periodic scheduler activation when cpu is idle in the current code, and if it works, I'll send a patch. Thanks 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) --=-eDutoBco3j8p+a60x/U/ 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 iEYEABECAAYFAlac3uEACgkQk4XaBE3IOsRokgCeONAgkyhnhzK8PNlrlw7zg59e nWIAn1Y+pIvwgzroRpm4d4OU4HqPFmbp =fggQ -----END PGP SIGNATURE----- --=-eDutoBco3j8p+a60x/U/-- --===============6174849530811643507== 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 --===============6174849530811643507==--