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

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Message-ID: <87fvbgnosx.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Mon, 12 Jan 2015 14:53:02 +0200
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

Peter Zijlstra <peterz@...radead.org> writes:

> 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?

Good point.

> 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.

Indeed we should, although I'd also like to have a force-override boot
time option for this.

Thanks,
--
Alex
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