Date: Sat, 15 Feb 2014 01:59:05 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Andrey Chernov <ache@FreeBSD.org>, John Baldwin <jhb@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: <52FEADC9.2040608@FreeBSD.org> In-Reply-To: <52FE9A5E.5050300@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>
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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. > } > ... > num_processors = sysconf(_SC_NPROCESSORS_CONF); > if (!opt_n_threads) > opt_n_threads = num_processors; > ... > In the thread itself: > struct thr_info *mythr = userdata; > int thr_id = mythr->id; > > if (num_processors > 1 && opt_n_threads % num_processors == 0) { > if (!opt_quiet) > applog(LOG_INFO, "Binding thread %d to cpu %d", > thr_id, thr_id % num_processors); > affine_to_cpu(thr_id, thr_id % num_processors); > } > -- Andriy Gapon
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