Messages in this thread | | | Date | Wed, 23 Jun 2010 10:15:23 +0200 | From | Jes Sorensen <> | Subject | Re: [PATCH V2 1/5] ara virt interface of perf to support kvm guest os statistics collection in guest os |
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On 06/23/10 03:13, Zhang, Yanmin wrote: > On Tue, 2010-06-22 at 09:58 +0200, Jes Sorensen wrote: >> Exposing the counters read-only would save a lot of overhead for sure. >>>> Question is if it is safe to drop overflow support? >>> Not safe. One of PMU hardware design objectives is to use interrupt or NMI to notify >>> software when event counter overflows. Without overflow support, software need poll >>> the PMU registers looply. That is not good and consumes more cpu resources. >> >> Here is an idea, how about having the overflow NMI in the host trigger a >> flag that causes the PMU register read to trap and get special handling? >> That way you could propagate the overflow back down to the guest. > That doesn't resolve the issue that guest os software has to poll register.
That is true, but it could set a flag through the para virt interface.
Cheers, Jes
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