Date: Wed, 18 May 2011 09:53:34 -0700 From: Garrett Cooper <yanegomi@gmail.com> To: Attilio Rao <attilio@freebsd.org> Cc: "freebsd-current@freebsd.org" <freebsd-current@freebsd.org>, Andriy Gapon <avg@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: [rfc] remove hlt_cpus et al sysctls and related code Message-ID: <BBCD9D8C-FCAF-4DE3-9F66-4B65AAABE67B@gmail.com> In-Reply-To: <BANLkTinVGrLoAOS_ZQ1YVB_Fw1cvf5kHyA@mail.gmail.com> References: <4DD3F662.9040603@FreeBSD.org> <BANLkTikOTe9ut3GFx0bhOernKandRGLhPg@mail.gmail.com> <BANLkTinVGrLoAOS_ZQ1YVB_Fw1cvf5kHyA@mail.gmail.com>
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On May 18, 2011, at 9:49 AM, Attilio Rao <attilio@freebsd.org> wrote: > 2011/5/18 Garrett Cooper <yanegomi@gmail.com>: >> On Wed, May 18, 2011 at 9:40 AM, Andriy Gapon <avg@freebsd.org> wrote: >>>=20 >>> I think that it is a well known fact that currently we do not have any s= upport for >>> dynamically offlining processors. Yet, we have some code that looks lik= e it does >>> provide that support and even provides a user interface to supposedly do= that. >>>=20 >>> What we don't currently do specifically: >>> - rebinding interrupts away from an offlined processor >>> - updating relevant cpu sets and masks >>> - protecting the above for concurrent access >>> - moving threads away from an offlined processor >>> - notifying potentially interested parties >>> - maybe more... >>>=20 >>> The code has been in this shape for a long while and I would dare to say= that it >>> never really worked, not in "production ready" sense anyway. >>> An example of troubles caused by using that code can be found e.g. in th= e >>> followups to the following PR: >>> http://www.freebsd.org/cgi/query-pr.cgi?pr=3D145385 >>> And also discussed here: >>> http://thread.gmane.org/gmane.os.freebsd.stable/74462/focus=3D74510 >>>=20 >>> I think that there already have been a proposal to remove the systcls an= d the >>> code. I would like to re-submit that proposal. >>> Removing that code would: >>> 1) prevent users from hurting themselves by executing broken code >>> 2) potentially make things easier for largeSMP project >>>=20 >>> Once we grow correct code for offlining CPUs, then we could re-introduce= the >>> sysctls without any problems. >>> While the offlining code doesn't seem terribly hard to develop, it's a b= ig piece >>> of work and requires time and effort. >>=20 >> What would be nice too (even though it might not be possible) is >> to make this more MI than it is today (i.e. sysctls that work for >> amd64, sparc64, etc), but that might be a pipe dream. >> Thanks! >> -Garrett >=20 > That is actually the purpose. We should have a real online/offline > system for hotplugging CPUs, not only tied to x86 hyperthreading. > The htt specific parts are mostly hacks that don't take into account > all the necessary handover for it. >=20 > Andryi, I'll look into the patch asap, but I'm in favor of this change for= sure. We use this internally at work still with a software config that uses 4B= SD so as long as there is an equivalent tunable, that's good enough for us m= oving forward. Thanks! -Garrett=
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