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: >>> >>> I think that it is a well known fact that currently we do not have any support for >>> dynamically offlining processors. Yet, we have some code that looks like it does >>> provide that support and even provides a user interface to supposedly do that. >>> >>> 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... >>> >>> 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 the >>> followups to the following PR: >>> http://www.freebsd.org/cgi/query-pr.cgi?pr=145385 >>> And also discussed here: >>> http://thread.gmane.org/gmane.os.freebsd.stable/74462/focus=74510 >>> >>> I think that there already have been a proposal to remove the systcls and 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 >>> >>> 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 big piece >>> of work and requires time and effort. >> >> 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 > > 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. > > 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 4BSD so as long as there is an equivalent tunable, that's good enough for us moving forward. Thanks! -Garretthelp
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