Hi Ren, Thank you for clarifying. I really do not have any more comments on the patch.
Regards, Prerna On Thu, Jul 9, 2015 at 12:27 PM, Ren, Qiaowei <qiaowei....@intel.com> wrote: > On Jul 7, 2015 15:51, Ren, Qiaowei wrote: > > > > > > On Jul 6, 2015 14:49, Prerna wrote: > > > >> On Sun, Jul 5, 2015 at 5:13 PM, Qiaowei Ren <qiaowei....@intel.com > >> <mailto:qiaowei....@intel.com> > wrote: > >> > >> > >> One RFC in > >> > https://www.redhat.com/archives/libvir-list/2015-June/msg01509.html > >> > >> CMT (Cache Monitoring Technology) can be used to measure the > >> usage of cache by VM running on the host. This patch will > >> extend the bulk stats API (virDomainListGetStats) to add this > >> field. Applications based on libvirt can use this API to achieve > >> cache usage of VM. Because CMT implementation in Linux kernel > >> is based on perf mechanism, this patch will enable perf event > >> for CMT when VM is created and disable it when VM is destroyed. > >> > >> > >> > >> > >> Hi Ren, > >> > >> One query wrt this implementation. I see you make a perf ioctl to > >> gather CMT stats each time the stats API is invoked. > >> > >> If the CMT stats are exposed by a hardware counter, then this implies > >> logging on a per-cpu (or per-socket ???) basis. > >> > >> This also implies that the value read will vary as the CPU (or socket) > >> on which it is being called changes. > >> > >> > >> Now, with this background, if we need real-world stats on a VM, we need > >> this perf ioctl executed on all CPUs/ sockets on which the VM ran. > >> Also, once done, we will need to aggregate results from each of these > >> sources. > >> > >> > >> In this implementation, I am missing this -- there seems no control > >> over which physical CPU the libvirt worker thread will run and collect > >> the perf data from. Data collected from this implementation might not > >> accurately model the system state. > >> > >> I _think_ libvirt currently has no way of directing a worker thread to > >> collect stats from a given CPU -- if we do, I would be happy to learn > >> about it :) > >> > > > > Prerna, thanks for your reply. I checked the CMT implementation in > > kernel, and noticed that the series implement new ->count() of pmu > > driver which can aggregate the results from each cpu if perf type is > > PERF_TYPE_INTEL_CQM . The following is the link for the patch: > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?i > > d=bfe1fc d2688f557a6b6a88f59ea7619228728bd7 > > > > So I guess that this patch just need to set right perf type and > "cpu=-1". Do you > > think this is ok? > > > > Hi Prerna, > > Do you have more comments on this patch series? I would be glad to update > my implementation. ^-^ > > Qiaowei > >
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