Date: Sat, 15 Feb 2014 02:36:14 +0400 From: Andrey Chernov <ache@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Ryan Stone <rysto32@gmail.com>, "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: <52FE9A5E.5050300@freebsd.org> In-Reply-To: <52FE93E6.6030705@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>
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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); } ... 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); } -- http://ache.vniz.net/
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