Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754155AbbDTR7c (ORCPT ); Mon, 20 Apr 2015 13:59:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48339 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753958AbbDTR7b (ORCPT ); Mon, 20 Apr 2015 13:59:31 -0400 Date: Mon, 20 Apr 2015 12:59:22 -0500 From: Clark Williams To: "Paul E. McKenney" Cc: Ingo Molnar , linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, a.p.zijlstra@chello.nl, akpm@linux-foundation.org, linux-rt-users@vger.kernel.org Subject: Re: [GIT RFC PULL rcu/urgent] Prevent Kconfig from asking pointless questions Message-ID: <20150420125922.35243e90@sluggy> In-Reply-To: <20150420170902.GU5561@linux.vnet.ibm.com> References: <20150416183812.GA5571@linux.vnet.ibm.com> <20150418130340.GA26931@gmail.com> <20150418133444.GD23685@linux.vnet.ibm.com> <20150418143238.GA2337@gmail.com> <20150419020541.GA5561@linux.vnet.ibm.com> <20150420113554.598e503f@sluggy> <20150420170902.GU5561@linux.vnet.ibm.com> Organization: Red Hat, Inc MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/MM8j6AKw6LkSSg+kBdtll1w"; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4043 Lines: 99 --Sig_/MM8j6AKw6LkSSg+kBdtll1w Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Mon, 20 Apr 2015 10:09:03 -0700 "Paul E. McKenney" wrote: > On Mon, Apr 20, 2015 at 11:35:54AM -0500, Clark Williams wrote: > > On Sat, 18 Apr 2015 19:05:42 -0700 > > "Paul E. McKenney" wrote: > > > > > > Real-time priority to use for RCU worker threads (RCU_KTHREAD_= PRIO) [0] (NEW)=20 > > > > >=20 > > > > > Indeed, Linus complained about this one. ;-) > > > >=20 > > > > :-) Yes, it's an essentially unanswerable question. > > > >=20 > > > > > This Kconfig parameter is a stopgap, and needs a real solution. = =20 > > > > > People with crazy-heavy workloads involving realtime cannot live= =20 > > > > > without it, but that means that most people don't have to care. = I=20 > > > > > have had solving this on my list, and this clearly increases its= =20 > > > > > priority. > > > >=20 > > > > So what value do they use, prio 99? 98? It might be better to offer= =20 > > > > this option as a binary choice, and set a given priority. If -rt=20 > > > > people complain then they might help us in solving it properly. > > >=20 > > > I honestly do not remember what priority they were using, it is > > > not in email, and I don't keep IRC logs that far back. Adding > > > linux-rt-users@vger.kernel.org on CC. > >=20 > > As I recall, we started out using fifo:1, but when you get heavy > > workloads running at higher fifo priorities, we wanted to boost the rcu > > worker threads over those workloads.=20 > >=20 > > Currently the irq threads default to fifo:50, so maybe a good > > default choice for the rcu threads on RT is fifo:49. That of course > > presumes rational behavior on the part of application developers.=20 > >=20 > > I seem to recall that you and I had a discussion about making this > > value a runtime knob in /sys but that didn't go anywhere. Do we need to > > crank that up again and just use the config as a default/starting > > value? If so then we could just default to fifo:1 and let sysadmins > > tweak the value to match up with the workload.=20 >=20 > The sysfs knob might be nice, but as far as I know nobody has been > complaining about it. >=20 > Besides, we already have the rcutree.kthread_prio=3D kernel-boot paramete= r. > So how about if the Kconfig parameter selects either SCHED_OTHER > (the default) or SCHED_FIFO:1, and then the boot parameter can be used > to select other values. Yeah, that will work.=20 >=20 > That said, if the lack of a sysfs knob has been causing real problems, > let's make that happen. I'll talk to the other RT-ers and get back to you on that. I suspect most folks would like it just to not have to reboot while tuning, but not sure it's worth the extra code.=20 Clark --Sig_/MM8j6AKw6LkSSg+kBdtll1w Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBAgAGBQJVNT5+AAoJEEersVlSw9NzZscQANdZS1+3/zU2BDhFidVuwhWC ypjTLwqe0HxDPkrhHIuBVsw2l700ggSodZniUA56uw90rq5j5kSKCWOoCuZkEITq lllatG5Wr1yS2Isl7n9yKWae9KjAcnnEJNxWiLwWOp4T3tkdRyT+ECOa73orRbw6 hvNWS377xVL9Gy39gS96BEa2sj4BF+R21FlUJzonRxOSUOmWUmLHU/pNSEgKC0vl QyUP6eHBJxMzQ/HkBzTGzeIPw0wZpgMgg4A8HQcbwG8OxAzDG9PlgOxBRGY55kHk tsc+Q+Fh7Fq2NJcpof/4HhQlJOXjBqx2gZSCqLAfw80v3UMy2Nbwq+3p56wuZO4f WpRJEFRawV6lRttqtaodmhWwvWYOnWeFz/YVXkCwr8xlEDdzj9rMmXPLGWYALGLs EsOpoe4o2YDpvzyyX2DZT0olnq7IvOEL7NFZOndQv2lMk76jpKpWsVmaxiw2oHDi mqpS9m86GjgGB9txJnOVafs8c/JjXKA9VaCPghiJ02UrQVIC4RTMvvGJwfBxJ4pn 5mZCMPIMTw2hQpwFdP1bGPn6N/NPxEB+dkqh1d1qrcriWFrYz4pVqBtmo5y8TEhB AYFzuC9j4/TAFPB+7veesJrh7Inv+klJ9qtJ78pMWQAOJcDh4hizfOolUUsOST2p LPjp82gIxNrInzU7PC8t =z6mQ -----END PGP SIGNATURE----- --Sig_/MM8j6AKw6LkSSg+kBdtll1w-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/