Messages in this thread | | | From | Alexander Shishkin <> | Subject | Re: [PATCH 0/4] perf, pt, coresight: AUX flags and VMX update | Date | Mon, 20 Feb 2017 18:31:28 +0200 |
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Arnaldo Carvalho de Melo <acme@kernel.org> writes:
> Em Mon, Feb 20, 2017 at 05:39:43PM +0200, Adrian Hunter escreveu: >> On 20/02/17 17:18, Alexander Shishkin wrote: >> > Alexander Shishkin <alexander.shishkin@linux.intel.com> writes: >> > >> >> With the vmm_exclusive=0, PT seems to be much more usable on BDW now. This >> >> patchset does three things: >> >> * adds a flag to PERF_RECORD_AUX, signalling that a transaction has gaps >> >> in it (due to VMX root mode kicking in), >> > >> > In the above context, will something like this be fine? > >> Looks fine to me. > >> Acked-by: Adrian Hunter <adrian.hunter@intel.com> >> >> > From: Alexander Shishkin <alexander.shishkin@linux.intel.com> >> > Subject: [PATCH] perf tools: Handle partial AUX records and print a warning > >> > This patch decodes the 'partial' flag in AUX records and prints >> > a warning to the user, so that they don't have to guess why their >> > PT traces contain gaps (or missing altogether): > >> >> Warning: >> >> AUX data had gaps in it 6 times out of 8! > > The above should be left for a more verbose mode? > >> >> Are you running a KVM guest in the background? > > The warning should be a bit more precise, as you said, tuning > vmm_exclusive is key here, i.e.: > > "Are you running a KVM guest in the background with > kvm_intel.vmm_exclusive=1?"
You'll still get gaps with vmm_exclusive=0 if you run perf record -a or if you try to trace the actual kvm.
> And that we can even figure out, its just a matter of reading: > > [root@jouet ~]# cat /sys/module/kvm_intel/parameters/vmm_exclusive > Y > > I have tested after setting that using: > > modprobe kvm_intel vmm_exclusive=n > > And I was able to get Intel PT records from a workload. > > So perhaps we can get this patch in, which improves the situation, and > then, on top of it do these extra checks and give proper hints, ok?
Sure.
Thanks, -- Alex
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