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

[Alexander Shishkin]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:

> On Wed, Oct 30, 2019 at 04:06:36AM +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.
>>      For precise_ip, it is the precise level in perf and set by perf command line in KVM guest, this may not reflect the accurate value (can be 0~3) here. Here set to 1 is used to allocate a counter for PEBS event and set the MSR_IA32_PEBS_ENABLE register. For PMU virtualization, KVM will trap the guest's write operation to PMU registers and allocate/free event counter from host if a counter enable/disable in guest. We can't always deduce the exact parameter of perf command line from the value of the guest writers to the register.
>
> Please, teach your MUA to wrap on 78 chars.
>
> The thing I really fell over is the gratuitous 'bool ? 1 : 0'. But yes,

Notice the .exclude_kernel assignment above that does the same thing the
other way around.

Regards,
--
Alex