linux-kernel - Re: [PATCH v8 12/14] x86: perf: intel

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Date:	Fri, 9 Jan 2015 15:09:47 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
	adrian.hunter@...el.com, markus.t.metzger@...el.com,
	mathieu.poirier@...aro.org, acme@...radead.org
Subject: Re: [PATCH v8 12/14] x86: perf: intel_pt: Intel PT PMU driver

On Fri, Nov 14, 2014 at 03:43:45PM +0200, Alexander Shishkin wrote:
> +static __init int pt_init(void)
> +{
> +	int ret, cpu, prior_warn = 0;
> +
> +	BUILD_BUG_ON(sizeof(struct topa) > PAGE_SIZE);
> +	get_online_cpus();
> +	for_each_online_cpu(cpu) {
> +		u64 ctl;
> +
> +		ret = rdmsrl_safe_on_cpu(cpu, MSR_IA32_RTIT_CTL, &ctl);
> +		if (!ret && (ctl & RTIT_CTL_TRACEEN))
> +			prior_warn++;
> +	}
> +	put_online_cpus();
> +
> +	ret = pt_pmu_hw_init();
> +	if (ret)
> +		return ret;
> +
> +	if (!pt_cap_get(PT_CAP_topa_output)) {
> +		pr_warn("ToPA output is not supported on this CPU\n");
> +		return -ENODEV;
> +	}
> +
> +	if (prior_warn)
> +		pr_warn("PT is enabled at boot time, traces may be empty\n");

Should we not also add_exclusive(pt) here?

Also, if its already enabled, should we not return ENODEV as well, no
saying who or what programmed it, we should not be touching it.

> +	if (!pt_cap_get(PT_CAP_topa_multiple_entries))
> +		pt_pmu.pmu.capabilities =
> +			PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_AUX_SW_DOUBLEBUF;
> +
> +	pt_pmu.pmu.capabilities	|= PERF_PMU_CAP_EXCLUSIVE | PERF_PMU_CAP_ITRACE;
> +	pt_pmu.pmu.attr_groups	= pt_attr_groups;
> +	pt_pmu.pmu.task_ctx_nr	= perf_hw_context;
> +	pt_pmu.pmu.event_init	= pt_event_init;
> +	pt_pmu.pmu.add		= pt_event_add;
> +	pt_pmu.pmu.del		= pt_event_del;
> +	pt_pmu.pmu.start	= pt_event_start;
> +	pt_pmu.pmu.stop		= pt_event_stop;
> +	pt_pmu.pmu.read		= pt_event_read;
> +	pt_pmu.pmu.setup_aux	= pt_buffer_setup_aux;
> +	pt_pmu.pmu.free_aux	= pt_buffer_free_aux;
> +	ret = perf_pmu_register(&pt_pmu.pmu, "intel_pt", -1);
> +
> +	return ret;
> +}
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