From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: [PATCH v3 15/15] docs: add MBA description in docs Date: Thu, 28 Sep 2017 18:56:07 +0200 Message-ID: <1506617767.5001.16.camel@citrix.com> References: <1504603957-5389-1-git-send-email-yi.y.sun@linux.intel.com> <1504603957-5389-16-git-send-email-yi.y.sun@linux.intel.com> <20170919113724.2pbo3csxzxqwymhv@dhcp-3-128.uk.xensource.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5340350367913249477==" Return-path: Received: from mail6.bemta6.messagelabs.com ([193.109.254.103]) by lists.xenproject.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dxc6r-0001zd-MR for xen-devel@lists.xenproject.org; Thu, 28 Sep 2017 16:56:25 +0000 In-Reply-To: <20170919113724.2pbo3csxzxqwymhv@dhcp-3-128.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" To: Roger Pau =?ISO-8859-1?Q?Monn=E9?= , Yi Sun Cc: kevin.tian@intel.com, wei.liu2@citrix.com, andrew.cooper3@citrix.com, ian.jackson@eu.citrix.com, julien.grall@arm.com, mengxu@cis.upenn.edu, jbeulich@suse.com, xen-devel@lists.xenproject.org, chao.p.peng@linux.intel.com, dgdegra@tycho.nsa.gov List-Id: xen-devel@lists.xenproject.org --===============5340350367913249477== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="=-1oBx66x2fjr9b5KTyame" --=-1oBx66x2fjr9b5KTyame Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2017-09-19 at 12:37 +0100, Roger Pau Monn=C3=A9 wrote: > On Tue, Sep 05, 2017 at 05:32:37PM +0800, Yi Sun wrote: > >=20 > > --- a/docs/man/xl.pod.1.in > > +++ b/docs/man/xl.pod.1.in > > @@ -1798,6 +1798,40 @@ processed. > > =C2=A0 > > =C2=A0=3Dback > > =C2=A0 > > +=3Dhead2 Memory Bandwidth Allocation > > + > > +Intel Skylake and later server platforms offer capabilities to > > configure and > > +make use of the Memory Bandwidth Allocation (MBA) mechanisms, > > which provides > > +OS/VMMs the ability to slow misbehaving apps/VMs or create > > advanced closed-loop >=20 > I don't get the 'closed-loop' thing again, but that might just be me > since I'm not a native speaker. >=20 > > +control system via exposing control over a credit-based throttling > > mechanism. > It goes together with 'control system'. In fact, 'closed-loop control system' is a concept from control theory (or system automation, or system theory... I've head it called in all these ways). It's when you want to control a system, or a process, and you do it by enclosing it in a "loop" in such a way that the n+1-th input to the process is influenced by the n-th output of the process itself. It's also called 'feedback-loop' or 'feedback-based control system'. Basically, you usually read/measure/sense the n-th output of the process, you compare it with some 'desired' value, and you use --as the process' n+1-th input-- some indication of how different the measured value was from the desired value. http://www.electronics-tutorials.ws/systems/closed-loop-system.html Alternatively, you have 'open-loop control systems', where there is no sensing of the output, and no feedback mechanism that would correct the input according to how things are actually going (i.e., someone says, there is no control!). http://www.electronics-tutorials.ws/systems/open-loop-system.html *I guess* what this means, in this context, is that, with both MBA and MBM, you can build a piece of software that, given a desired memory bandwidth usage, for a certain domain, sets MBA accordingly, then monitors what the domain is actually getting, and use the difference between that and the desired value to drive the new value to be set, using MBA again. Like, if it's getting less, give it _some_ more, if it's getting more, give it _some_ less (where both the _some_-s are coefficients). Ideally, after initial spikes and fluctuations (which depends on the coefficients, and on which one can do math, still using control theory concepts), happening, e.g., when the workload inside the VM changes, the bandwidth utilization will settle at the desired point. All that being said, I'd say that either more details are given (or a link is put here, pointing to a whitepaper or in general a place where a full description of the solution can be found), or it's probably better to drop the 'close-loop' reference, and explain how MBA can be useful in another way. Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-1oBx66x2fjr9b5KTyame 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 v2 iQIcBAABCAAGBQJZzSmoAAoJEBZCeImluHPu+E8P/jw9mRbjG2Ow8Hft3n3QGGSJ 62pnsLD1iVrmrWLbxUF3AKvkdCbenYtZv62mn712LOwmFDGn6PP3iT99OTnBly1C SVl+iQT6zD2/CYh55pq0crptTt5YN++DnAHwjOnFXUiNzQMscRya3QTr7d54OYrG ghD25bmFwuk5SRJ9UgkyiomYPlXv4G2xFZ91tDEyAJV6nbgFDDZMYhAgqzTZmoWw Pwlzd42tGUnMfDVV6wb+fogqx4n04TyvTdv1iGVl5dePsV0Cl1zq1Cs/+6AA+VJ7 wG7ItIqOVz9t3YFdM+qFaN7Y7i35eR2G75jZgfzaWITicBKBx+ZVoQOJSncxRlrn EwebOs89iC9M3DHi5cg4aqzOUGZo47sr72JRVlJCi/k+ERJcN+nS3sQK7fUlH00B t31Oh1OiLGGSYsel6NHtHiAuA6CFa7EBFBsY2fCmAJO29XH0j2/zZ/IUt6x9wzq9 ZSfp4vdTxwlyDAa7xZcQ2JCpKDWSYMst2JqOt7YCaTOfYHtcz0QlBUO7fiavzCfh SEgUnT5upgSnECHH7MslkNj1MSVmkTsZLNcljOf/+IE5ryS/d9RzNjYhMmDhRKTG FfIytKSg3rJpOszNibJKZXBAesl9iF7NbvvpZ+VnzsaohvOOrPx3GVY1EMLKvbq0 9gdKnEyf60s/bq3ZNewu =jZND -----END PGP SIGNATURE----- --=-1oBx66x2fjr9b5KTyame-- --===============5340350367913249477== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: inline X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KWGVuLWRldmVs IG1haWxpbmcgbGlzdApYZW4tZGV2ZWxAbGlzdHMueGVuLm9yZwpodHRwczovL2xpc3RzLnhlbi5v cmcveGVuLWRldmVsCg== --===============5340350367913249477==--