linux-kernel - Re: [PATCH 1/1] perf/x86/intel: Add extended event constraints for Knights Landing

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Date:	Fri, 24 Jun 2016 10:04:32 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	"Odzioba, Lukasz" <lukasz.odzioba@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"Liang, Kan" <kan.liang@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"acme@...nel.org" <acme@...nel.org>,
	"alexander.shishkin@...ux.intel.com" 
	<alexander.shishkin@...ux.intel.com>, "bp@...e.de" <bp@...e.de>,
	"Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>
Subject: Re: [PATCH 1/1] perf/x86/intel: Add extended event constraints for
 Knights Landing

Hi,

On Fri, Jun 24, 2016 at 7:54 AM, Odzioba, Lukasz
<lukasz.odzioba@...el.com> wrote:
> On Tuesday, June 21, 2016 11:38 AM, Peter Zijlstra wrote:
>> Yes, that is the intent, but how is this achieved? I'm not sure I see
>> how the patch ensure this.
>
> If you are confused, then it is likely that I did something wrong here.
> Let me explain myself.
>
> We already have a mechanism to create static constraints which limit events
> to given PMCs via event code filtering. Such constraints are later obeyed by event
> scheduler to assure that. Scheduler bases its decisions on idxmsk to place events
> on the right PMC.
>
> We can think of OFFCORE_RESPONSE/config1 values as an extension
> of event code making it 128bit long (code+extended code).
>
> Emask is extended code logically ANDed with extended code mask (analogy to
> c->cmask and c->code), we could add separate values here, but I didn't see a real use
> for it right now.
>
> Event code is used only in x86_get_event_constraints, so we have to extend event
> code matching check there to use config1 against our new emask.
> If constraint code matches event code and constraint has non empty extended
> code we check it against config1, if config1 uses one of the bits defined in emask
> we return constraint as if would be normal 64bit-code constraint, scheduler will take
> care of the rest.
>
>> Also, intel_get_event_constraints() has a path where it copies the
>> constraint, should it not also copy the new field?
>
> Since event code is not used anywhere except x86_get_event_constraints,
> so extended code is also not needed there.
>
> To verify that it works as I expect I added printk's to x86_assign_hw_event
> to see selected PMC.
>
What happens if I do in one run:
   2- cpu/event=0xb7,umask=0x1,offcore_rsp=0x100/u,cpu/event=0xb7,umask=0x2,offcore_rsp=0x100/k
   3- cpu/event=0xb7,umask=0x1,offcore_rsp=1ull<<38/,cpu/event=0xb7,umask=0x1,offcore_rsp=0x1/
   4- cpu/event=0xb7,umask=0x1,offcore_rsp=1ull<<38/,cpu/event=0xb7,umask=0x1,offcore_rsp=1ull<<38|1/

You get the shared constraints BEFORE the static constraints. So if
you've gone thru intel_alt_er() , then you should still be fine. In
case of counter conflict during scheduling the shared regs are free in
put_event_constraints(). So it should be fine there too.