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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 09/12/2014 11:30 AM, Jan Beulich wrote:
>>>> On 12.09.14 at 17:03, <boris.ostrovsky@oracle.com> 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.

-boris