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SubjectRe: [PATCH] perf/x86: descriptive failure messages for PMU init
Date
Hi Peter,

Peter Zijlstra <peterz@infradead.org> writes:

> On Fri, Apr 12, 2019 at 03:09:17PM -0400, Bandan Das wrote:
>>
>> There's a default warning message that gets printed, however,
>> there are various failure conditions:
>> - a msr read can fail
>> - a msr write can fail
>> - a msr has an unexpected value
>> - all msrs have unexpected values (disable PMU)
>>
>> Also, commit commit 005bd0077a79 ("perf/x86: Modify error message in
>> virtualized environment") completely removed printing the msr in
>> question but these messages could be helpful for debugging vPMUs as
>> well. Add them back and change them to pr_debugs, this keeps the
>> behavior the same for baremetal.
>>
>> Lastly, use %llx to silence checkpatch
>
> Yuck... if you're debugging a hypervisor, you can bloody well run your
> own kernel with additional print slattered around.
>
> The whole make an exception for virt bullshit was already pushing it,
> this is just insane.
>

The only virt specific parts are the pr_debugs which I can remove and
replace with unconditional pr_err()s as suggested by Jiri. Is that ok ?

Bandan

>> @@ -266,12 +282,30 @@ static bool check_hw_exists(void)
>> return true;
>>
>> msr_fail:
>> - if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
>> + if (virt)
>> pr_cont("PMU not available due to virtualization, using software events only.\n");
>> - } else {
>> - pr_cont("Broken PMU hardware detected, using software events only.\n");
>> - pr_err("Failed to access perfctr msr (MSR %x is %Lx)\n",
>> - reg, val_new);
>> + switch (status) {
>> + case READ_FAIL:
>> + if (virt)
>> + pr_debug("Failed to read perfctr msr (MSR %x)\n", reg);
>> + else
>> + pr_err("Failed to read perfctr msr (MSR %x)\n", reg);
>> + break;
>> + case WRITE_FAIL:
>> + if (virt)
>> + pr_debug("Failed to write perfctr msr (MSR %x, wrote: %llx, read: %llx)\n",
>> + reg, val, val_new);
>> + else
>> + pr_err("Failed to write perfctr msr (MSR %x, wrote: %llx, read: %llx)\n",
>> + reg, val, val_new);
>> + break;
>> + case PMU_FAIL:
>> + /* fall through for default message */
>> + default:
>> + if (virt)
>> + pr_debug("Broken PMU hardware detected, using software events only.\n");
>> + else
>> + pr_cont("Broken PMU hardware detected, using software events only.\n");
>> }

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