can the scheduler decide to schedule an interrupted but runnable thread on another CPU core? What are the implications for code?
John-Mark Gurney
jmg at funkthat.com
Sat Feb 15 00:11:02 UTC 2014
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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