From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41BDAC49ED6 for ; Wed, 11 Sep 2019 16:03:19 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 197AC20838 for ; Wed, 11 Sep 2019 16:03:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 197AC20838 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1i854V-0007Cs-IW; Wed, 11 Sep 2019 16:02:19 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1i854T-0007Cm-MA for xen-devel@lists.xenproject.org; Wed, 11 Sep 2019 16:02:17 +0000 X-Inumbo-ID: 85cc00fe-d4ad-11e9-978d-bc764e2007e4 Received: from mx1.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 85cc00fe-d4ad-11e9-978d-bc764e2007e4; Wed, 11 Sep 2019 16:02:15 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 72569B67A; Wed, 11 Sep 2019 16:02:14 +0000 (UTC) Message-ID: <3b82cd499348c140a6c86b1969f7891a0d011b8c.camel@suse.com> From: Dario Faggioli To: Juergen Gross , Jan Beulich Date: Wed, 11 Sep 2019 18:02:11 +0200 In-Reply-To: References: <20190809145833.1020-1-jgross@suse.com> <20190809145833.1020-9-jgross@suse.com> <22dc77b0-7ffa-a7ba-c3e5-14833f0b0b72@suse.com> <9a48c9ac-1aba-2102-d444-a135a588b30f@suse.com> Organization: SUSE User-Agent: Evolution 3.32.4 MIME-Version: 1.0 Subject: Re: [Xen-devel] [PATCH v2 08/48] xen/sched: switch vcpu_schedule_lock to unit_schedule_lock X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Konrad Rzeszutek Wilk , George Dunlap , Andrew Cooper , Tim Deegan , Julien Grall , Meng Xu , xen-devel@lists.xenproject.org, Ian Jackson Content-Type: multipart/mixed; boundary="===============6479768484113681813==" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" --===============6479768484113681813== Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-AWd6J0Fvsa8s8S4sxOXu" --=-AWd6J0Fvsa8s8S4sxOXu Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2019-09-04 at 17:02 +0200, Juergen Gross wrote: > On 04.09.19 16:54, Jan Beulich wrote: > > On 04.09.2019 16:41, Juergen Gross wrote: > > > On 04.09.19 16:02, Jan Beulich wrote: > > > >=20 > > > > At the example of this: The more coarse granularity of the lock > > > > means that no two vCPU-s within a unit can obtain their > > > > runstate > > > > in parallel. While this may be acceptable for core scheduling, > > > > I'm afraid it's too restrictive for sockets or nodes as units. > > > > Therefore I think this lock needs to either be split (I'm not > > > > sure that's feasible) or become an r/w lock. > > >=20 > > > You are aware that even today with credit2 all cpus of a socket > > > share > > > the same lock (if not modified via boot parameter)? > >=20 > > No, I wasn't (explicitly; I could have deduced it). Not very > > helpful, > > I'm afraid, but unlikely to be bad enough to go back to credit1 > > (but > > people having an issue with this could be told to switch back). >=20 > Well, performance tests have shown that this is the most performant > setting. And before going back to credit1 they still can use another > lock setting (core or cpu). >=20 Yeah, but it's not only locking. It's the entire load balancing mechanism. And yes, the scalability test we did showed that per-socket runqueues was better. I think it is possible to improve locking scalability of Credit2 (or, at least, I have some ideas.. but no code yet). All that being said, I think it would be rather difficult to implement sub-unit locking. And I don't think it's worth to do it right now, out of concerns of potential scalability issues for socket-scheduling. We're discussing about merging core-scheduling, but keeping it disabled for now. We're not even sure if/when people will start to use *it*. I currently don't see much use cases for socket-scheduling (although it is indeed cool that we get the implementation basically for free!), and hence I won't block patches or complicate the work for something like that. Regards --=20 Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <> (Raistlin Majere) --=-AWd6J0Fvsa8s8S4sxOXu Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEES5ssOj3Vhr0WPnOLFkJ4iaW4c+4FAl15GoQACgkQFkJ4iaW4 c+53vQ/9EXlHRm06WlhoBDIIwEgNH3UUiNU745eD3QY709V46tYnRp9xDHpn14EX t5B5tAs5XX6fHUV79KMUevaV8AYLqOEllDaoWMxyqt+XHlEA+XPkFGlCDr42CA6z C31NEaJPEIc2etCQadGvJMMQUDi5Fd5Tp4Krpbj30dZEUoYoiRuMKgTvwkLljb3l s8o7HLR7E/oZ4PIihpeB1te+v78a87mHQbdVjs1KGHl77j48sUbwMQS4gZuIIUuV jLvyV5oECFeMEnvIzvf12P1iR4axFe4222VAMD4tbIITXaAglWjJmiFCQcifmA5+ t327cwZ0HZ0P3+rEnQr8Uo7ek4tGqacZBYLvnW4aJB9ndD3kaMpwXRwP1tqQjmzc /dt8XbAOqPaJfp6s2WXWjFKiuaXQFXONmPGJYmIMbwAlwFcBIImbQF+IJ3B9jpg2 MgDQootjeMxryLPSPK8AcibMgej5sVnRa3GQ2PoqYFlQymcAWhaWfeXe8b4ogCaI wsJx/22qYdeg0Cy7HXH6FUoYBGvkCPJWftnhiUX/S/E8viTAGeh1h3LWoxbKaiJE 8kzUXc7yvb1d1OA5VCIhy9hO4w2fjdQP+ygAmdxkie0US49U3WgIcPixdPybpEBk 5T09u3SZuAsqCZOYK8sxoqmnkOnzediCoxQThZ5GqqeltKHRhIk= =l2pD -----END PGP SIGNATURE----- --=-AWd6J0Fvsa8s8S4sxOXu-- --===============6479768484113681813== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: inline X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KWGVuLWRldmVs IG1haWxpbmcgbGlzdApYZW4tZGV2ZWxAbGlzdHMueGVucHJvamVjdC5vcmcKaHR0cHM6Ly9saXN0 cy54ZW5wcm9qZWN0Lm9yZy9tYWlsbWFuL2xpc3RpbmZvL3hlbi1kZXZlbA== --===============6479768484113681813==--