linux-kernel - RE: [PATCH v1 3/8] KVM: x86: Allocate performance counter for PEBS event

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Message-ID: <87o8xyg2f1.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Wed, 30 Oct 2019 08:42:10 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     "Kang\, Luwei" <luwei.kang@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini\@redhat.com" <pbonzini@...hat.com>,
        "rkrcmar\@redhat.com" <rkrcmar@...hat.com>,
        "Christopherson\, Sean J" <sean.j.christopherson@...el.com>,
        "vkuznets\@redhat.com" <vkuznets@...hat.com>,
        "wanpengli\@tencent.com" <wanpengli@...cent.com>,
        "jmattson\@google.com" <jmattson@...gle.com>,
        "joro\@8bytes.org" <joro@...tes.org>,
        "tglx\@linutronix.de" <tglx@...utronix.de>,
        "mingo\@redhat.com" <mingo@...hat.com>,
        "bp\@alien8.de" <bp@...en8.de>, "hpa\@zytor.com" <hpa@...or.com>,
        "x86\@kernel.org" <x86@...nel.org>,
        "ak\@linux.intel.com" <ak@...ux.intel.com>,
        "thomas.lendacky\@amd.com" <thomas.lendacky@....com>,
        "acme\@kernel.org" <acme@...nel.org>,
        "mark.rutland\@arm.com" <mark.rutland@....com>,
        "jolsa\@redhat.com" <jolsa@...hat.com>,
        "namhyung\@kernel.org" <namhyung@...nel.org>,
        alexander.shishkin@...ux.intel.com
Subject: RE: [PATCH v1 3/8] KVM: x86: Allocate performance counter for PEBS event

"Kang, Luwei" <luwei.kang@...el.com> writes:

>> >  static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>> >  				  unsigned config, bool exclude_user,
>> >  				  bool exclude_kernel, bool intr,
>> > -				  bool in_tx, bool in_tx_cp)
>> > +				  bool in_tx, bool in_tx_cp, bool pebs)
>> >  {
>> >  	struct perf_event *event;
>> >  	struct perf_event_attr attr = {
>> > @@ -111,9 +111,12 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
>> >  		.exclude_user = exclude_user,
>> >  		.exclude_kernel = exclude_kernel,
>> >  		.config = config,
>> > +		.precise_ip = pebs ? 1 : 0,
>> > +		.aux_output = pebs ? 1 : 0,
>> 
>> srsly?
>
> Hi Peter,
>     Thanks for review. For aux_output, I think it should be set 1 when the guest wants to enabled PEBS by Intel PT.

attr.aux_output==1 means your group leader should be an intel_pt event
for this to succeed. Luckily for this instance,
perf_event_create_kernel_counter() doesn't actually check the
attr.aux_output.

Also, does 'bool pebs' mean PEBS-via-PT or just a PEBS counter? Or does
it mean that in kvm it's the same thing?

Regards,
--
Alex