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From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Robert Richter <rric@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>, Andi Kleen <ak@linux.intel.com>,
        kan.liang@intel.com, adrian.hunter@intel.com,
        markus.t.metzger@intel.com, mathieu.poirier@linaro.org,
        acme@infradead.org
Subject: Re: [PATCH v8 12/14] x86: perf: intel_pt: Intel PT PMU driver
In-Reply-To: <20150109140947.GN3337@twins.programming.kicks-ass.net>
References: <1415972627-37514-1-git-send-email-alexander.shishkin@linux.intel.com> <1415972627-37514-13-git-send-email-alexander.shishkin@linux.intel.com> <20150109140947.GN3337@twins.programming.kicks-ass.net>
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Date: Mon, 12 Jan 2015 14:53:02 +0200
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Peter Zijlstra <peterz@infradead.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