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Re: [Xen-devel] [PATCH v10 11/20] x86/VPMU: Interface for setting PMU mode and flags
- To: "Boris Ostrovsky" <boris.ostrovsky@xxxxxxxxxx>
- From: "Jan Beulich" <JBeulich@xxxxxxxx>
- Date: Fri, 12 Sep 2014 16:30:13 +0100
- Cc: tim@xxxxxxx, kevin.tian@xxxxxxxxx, keir@xxxxxxx, suravee.suthikulpanit@xxxxxxx, andrew.cooper3@xxxxxxxxxx, eddie.dong@xxxxxxxxx, xen-devel@xxxxxxxxxxxxx, Aravind.Gopalakrishnan@xxxxxxx, jun.nakajima@xxxxxxxxx
- Delivery-date: Fri, 12 Sep 2014 15:30:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
>>> 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)?
Jan
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