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

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Date:   Wed, 30 Oct 2019 10:51:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kang, Luwei" <luwei.kang@...el.com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "acme@...nel.org" <acme@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v1 3/8] KVM: x86: Allocate performance counter for PEBS
 event

On Wed, Oct 30, 2019 at 06:49:42AM +0000, Kang, Luwei wrote:
> > >> >  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?
> 
> It is the same thing. Allocate a counter for PEBS event and use PEBS-via-PT.

It is not the same thing, obviously. It strictly means pebs-over-pt
here.