From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: [PATCH v4] xen: sched: convert RTDS from time to event driven model Date: Wed, 3 Feb 2016 13:30:29 +0100 Message-ID: <1454502629.9227.268.camel@citrix.com> References: <1454301176-7131-1-git-send-email-tiche@seas.upenn.edu> <1454425705.9227.176.camel@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0911773666925218772==" Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1aQwa9-0007mL-MD for xen-devel@lists.xenproject.org; Wed, 03 Feb 2016 12:30:49 +0000 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: Meng Xu Cc: "xen-devel@lists.xenproject.org" , Tianyang Chen , George Dunlap , Dagaen Golomb , Meng Xu List-Id: xen-devel@lists.xenproject.org --===============0911773666925218772== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-9H+fII5tjvkBXhWjwqlh" --=-9H+fII5tjvkBXhWjwqlh Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2016-02-02 at 22:33 -0500, Meng Xu wrote: > On Tue, Feb 2, 2016 at 10:08 AM, Dario Faggioli > wrote: > >=C2=A0 > > Is it ok to kill the replenishment in this case? > >=20 > > This is a genuine question. What does the dynamic DS algorithm that > > you're trying to implement here says about this? Meng, maybe you > > can > > help here? >=20 >=20 > Based on the DS algorithm (in theory), each VCPU should have its > budget replenished at the beginning of its next period. >=20 > However, we are thinking that when a VCPU is put to sleep, no one is > supposed to use it. Do we really need to keep updating the VCPU's > budget? Can we just update the VCPU's budget when it is waken up > later? This could potentially save some implementation overhead, > IMHO. > That's why we decided not to update the budget of VCPUs that are put > into sleep. >=C2=A0 > > Is it ok to do this _because_ you then handle the situation of a > > replenishment having to had happened while the vcpu was asleep in > > rt_vcpu_wake (the '(now>=3Dsvc->cur_deadline)' thing)? Yes... it > > probably > > is ok for that reason... >=20 >=20 > Yes, exactly. We hope this could reduce the frequency of invoking the > replenishment timer when the system is (kind of) idle. >=20 I see what you mean. I wonder, however, given how big and complicated this re-structuring we are doing is, whether it would not be easier to just leave this optimization for the future, and just implement the algorithm in the new event-driven fashion, as first step. Early optimization is known to be a bad thing in software. Note that I'm not saying that the optimization should happen in 6 months, it can be patch number 2 of the same series doing the event- driven transformation... I'm just saying that we should probably have a patch 1 which does only that, for ease of both =C2=A0doing and reviewing. Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-9H+fII5tjvkBXhWjwqlh 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 iEYEABECAAYFAlax8uUACgkQk4XaBE3IOsQKFwCgr0vmsmc30e1jc09VgbRY9Bc0 ayYAn1Q0SxHZTb9mMX4lxmyCkbuUA9ep =cZRJ -----END PGP SIGNATURE----- --=-9H+fII5tjvkBXhWjwqlh-- --===============0911773666925218772== 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 --===============0911773666925218772==--