linux-kernel - Re: [PATCH 2/2] perf/x86/amd: Add support for Large Increment per Cycle Events

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Date:   Fri, 20 Dec 2019 13:09:45 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Stephane Eranian <eranian@...gle.com>,
        Martin Liška <mliska@...e.cz>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH 2/2] perf/x86/amd: Add support for Large Increment per
 Cycle Events

On Thu, Nov 14, 2019 at 12:37:20PM -0600, Kim Phillips wrote:

I still hate the naming on this, "large increment per cycle" is just a
random bunch of words collected by AMD marketing or somesuch. It doesn't
convey the fundamental point that counters get paired. So I've done a
giant bunch of search and replace on it for you.

> @@ -621,6 +622,8 @@ void x86_pmu_disable_all(void)
>  			continue;
>  		val &= ~ARCH_PERFMON_EVENTSEL_ENABLE;
>  		wrmsrl(x86_pmu_config_addr(idx), val);
> +		if (is_large_inc(hwc))
> +			wrmsrl(x86_pmu_config_addr(idx + 1), 0);
>  	}
>  }
>  

See, the above makes sense, it doesn't assume anything about where
config for idx and config for idx+1 are, and then here:

> @@ -855,6 +871,9 @@ static inline void x86_pmu_disable_event(struct perf_event *event)
>  	struct hw_perf_event *hwc = &event->hw;
>  
>  	wrmsrl(hwc->config_base, hwc->config);
> +
> +	if (is_large_inc(hwc))
> +		wrmsrl(hwc->config_base + 2, 0);
>  }

You hard-code the offset as being 2. I fixed that for you.

> @@ -849,14 +862,19 @@ int perf_assign_events(struct event_constraint **constraints, int n,
>  			int wmin, int wmax, int gpmax, int *assign)
>  {
>  	struct perf_sched sched;
> +	struct event_constraint *c;
>  
>  	perf_sched_init(&sched, constraints, n, wmin, wmax, gpmax);
>  
>  	do {
>  		if (!perf_sched_find_counter(&sched))
>  			break;	/* failed */
> -		if (assign)
> +		if (assign) {
>  			assign[sched.state.event] = sched.state.counter;
> +			c = constraints[sched.state.event];
> +			if (c->flags & PERF_X86_EVENT_LARGE_INC)
> +				sched.state.counter++;
> +		}
>  	} while (perf_sched_next_event(&sched));
>  
>  	return sched.state.unassigned;

I'm still confused by this bit. AFAICT it serves no purpose.
perf_sched_next_event() will reset sched->state.counter to 0 on every
pass anyway.

I've deleted it for you.

> @@ -926,10 +944,14 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
>  			break;
>  
>  		/* not already used */
> -		if (test_bit(hwc->idx, used_mask))
> +		if (test_bit(hwc->idx, used_mask) || (is_large_inc(hwc) &&
> +		    test_bit(hwc->idx + 1, used_mask)))
>  			break;
>  
>  		__set_bit(hwc->idx, used_mask);
> +		if (is_large_inc(hwc))
> +			__set_bit(hwc->idx + 1, used_mask);
> +
>  		if (assign)
>  			assign[i] = hwc->idx;
>  	}

This is just really sad.. fixed that too.

Can you verify the patches in:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/amd

work?