Implement sched_[gs]etaffinity()
Corinna Vinschen
corinna-cygwin@cygwin.com
Wed Apr 17 07:57:00 GMT 2019
On Apr 16 21:31, Mark Geisert wrote:
> On Tue, 16 Apr 2019, Corinna Vinschen wrote:
> > On Apr 16 01:19, Mark Geisert wrote:
> > > Anybody know if one can
> > > depend on the group membership of the first processor group to apply to all
> > > groups?
> >
> > Maybe https://go.microsoft.com/fwlink/p/?linkid=147914 helps?
> >
> > "If the number of logical processors exceeds the maximum group size,
> > Windows creates multiple groups by splitting the node into n groups,
> > where the first n-1 groups have capacities that are equal to the group
> > size."
>
> Great; thanks for that.
>
> > [...]
> > Therefore:
> >
> > WORD cpu_group = cpu_number / num_cpu_per_group;
> > KAFFINITY cpu_mask = 1L << (cpu_number % num_cpu_per_group);
> >
> > That also means the transposition between the groupless linux system
> > and the WIndows system is fairly easy.
>
> Yes, dealing with an array of unsigned longs vs bitblt ops FTW.
>
> > > (6) On Linux, processor affinity is inherited across fork() and execve().
> > > I'll need to ensure Cygwin's implementation of those calls handle affinity
> > > the same way.
> >
> > Just passing the INHERIT_PARENT_AFFINITY flag to CreateProcess{AsUser}
> > should do the trick.
>
> OK. Hope so.
Well, nope, sorry. Per MSDN:
The process inherits its parent's affinity. If the parent process has
threads in more than one processor group, the new process inherits the
group-relative affinity of an arbitrary group in use by the parent.
Also important: This value is not supported on Vista, so it should
only be used if wincap.has_processor_groups() is true.
> (7), to make a prime number: I don't see any need for the Cygwin DLL to keep
> any affinity info (process or thread) or processor group membership info
> around, do you? I believe the sched_get/setaffinity functions will do
> whatever Windows ops they need to do on the fly based on the args passed in.
> That allows the user to do Windows affinity ops at will outside of Cygwin
> without screwing up any Cygwin-maintained context.
I agree. Additionally I think we should not overvalue affinity
inheritance. Specifying INHERIT_PARENT_AFFINITY should be enough
for a start. There's no reason for overkill.
Thanks,
Corinna
--
Corinna Vinschen
Cygwin Maintainer
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