Re: libgo patch committed: Support NumCPU on more platforms

[Ian Lance Taylor <iant at google dot com>]

On Tue, Aug 7, 2012 at 5:21 AM, Richard Earnshaw <rearnsha@arm.com> wrote:
>
> Wouldn't it be more useful on Linux to check the task's affinity
> settings?  Then when a task is locked to a limited set of cores it won't
> overload those cores with threads.

Good question.  I'm not sure.  This patch does not change the number
of threads that the Go runtime will use, so your particular concern is
not an issue.  This patch changes the return value of the standard
library function runtime.NumCPU.  And if the number of processors is >
1, it tweaks some of the runtime code, e.g., to use a limited time
spin lock (if the number of processors == 1, a spin lock is pointless,
and the code moves straight to a futex).  I guess that if the process
is restricted to a single processor by affinity, then it might be
better to be aware of that and skip the spin lock.  But I'm not sure
what the return value of runtime.NumCPU should be.  It's documented as
"NumCPU returns the number of logical CPUs on the local machine."

Ian