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Re: [Xen-devel] [PATCH v10 11/20] x86/VPMU: Interface for setting PMU mode and flags

On 09/12/2014 11:30 AM, Jan Beulich wrote:
On 12.09.14 at 17:03, <boris.ostrovsky@xxxxxxxxxx> wrote:
My concern is that on a very large system we may be getting lots of
preemptions and thus this will be failing for the sysadmin somewhat
often and without clear reason. (I am basing this assumption on the fact
that I am currently looking at a ~200CPU box with gobs of memory and
some operations that use contuations get preempted very often. Hundreds
of times. I don't remember seeing this on "regular" systems).
Yeah, quite likely due to IPI counts growing approximately with the
square of the CPU count.

We've been considering adding a "minimum amount of progress"
mechanism to various places where preemption can (at least under
some conditions) be observed on every iteration. Perhaps along
with having the 5s timeout you also want a minimum amount of
time during which you don't check for preemption (yet)?

Yes, I can do that. Something like half second?

This is a very infrequent operation that can only be done in dom0 by a sysadmin so even if this seems a bit too long I think it's safe enough.


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