Date: Fri, 14 Feb 2014 16:11:00 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Andriy Gapon <avg@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: can the scheduler decide to schedule an interrupted but runnable thread on another CPU core? What are the implications for code? Message-ID: <20140215001100.GS34851@funkthat.com> In-Reply-To: <52FEADC9.2040608@FreeBSD.org> References: <CAJ-Vmo=7Nz1jqXy%2BrTQ7u9_ZP7jeFOKUJxU1O51tYJjvTUmWTg@mail.gmail.com> <201402141318.44743.jhb@freebsd.org> <52FE5FBF.3090104@freebsd.org> <201402141410.29325.jhb@freebsd.org> <52FE93E6.6030705@freebsd.org> <52FE9A5E.5050300@freebsd.org> <52FEADC9.2040608@FreeBSD.org>
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Andriy Gapon wrote this message on Sat, Feb 15, 2014 at 01:59 +0200: > on 15/02/2014 00:36 Andrey Chernov said the following: > > On 15.02.2014 2:08, Andrey Chernov wrote: > >> On 14.02.2014 23:10, John Baldwin wrote: > >> > >>>> Due to this bug, not fixed yet, the real picture is more complex: > >>>> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/163585 > >>> > >>> Eh, that bug report has no useful details, as in, it doesn't list the > >>> actual commands run. If you do 'cpuset -l 6 -s 1' to force all > >>> processes to only use CPU6, then yes, of course the other CPUs are idle > >>> because that's what you _asked_ for. AFAICT, that is all the original > >>> reporter did. At work we regularly add and remove CPUs from the > >>> default set (set 1) on hundreds of machines every day with ULE without > >>> any issues. > >> > >> Probably original report lack certain commands, but I provide the link > >> to the port which reproduces this bug too. All threads there are > >> assigned to the _different_ CPUs and appears as result on single one > >> with SCHED_ULE (not with SCHED_4BSD). And it is what original reporter > >> mean too. It surely happens, maybe not the first time, but on 2nd-3rd. > >> It means that cpuset_setaffinity() is completely broken form SCHED_ULE > >> at least for 3 years. > >> > > > > This is code example from cpuminer port, in case you are interested, it is very simple: > > > > static inline void affine_to_cpu(int id, int cpu) > > { > > cpuset_t set; > > CPU_ZERO(&set); > > CPU_SET(cpu, &set); > > cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_CPUSET, -1, sizeof(cpuset_t), &set); > > I think that CPU_WHICH_TID should have been used here. I agree... cpuset(2): The which argument determines how the value of id is interpreted and is of type cpuwhich_t. The which argument may have the following values: CPU_WHICH_TID id is lwpid_t (thread id) CPU_WHICH_PID id is pid_t (process id) CPU_WHICH_CPUSET id is a cpusetid_t (cpuset id) CPU_WHICH_IRQ id is an irq number An id of '-1' may be used with a which of CPU_WHICH_TID, CPU_WHICH_PID, or CPU_WHICH_CPUSET to mean the current thread, process, or current thread's cpuset. All cpuset syscalls allow this usage. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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