linux-kernel - Re: [PATCH v7 07/12] perf/x86: no counter allocation support

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Date:   Tue, 09 Jul 2019 19:36:53 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, ak@...ux.intel.com, kan.liang@...el.com,
        mingo@...hat.com, rkrcmar@...hat.com, like.xu@...el.com,
        jannh@...gle.com, arei.gonglei@...wei.com, jmattson@...gle.com
Subject: Re: [PATCH v7 07/12] perf/x86: no counter allocation support

On 07/09/2019 05:43 PM, Peter Zijlstra wrote:
> That's almost a year ago; I really can't remember that and you didn't
> put any of that in your Changelog to help me remember.
>
> (also please use: https://lkml.kernel.org/r/$msgid style links)

OK, I'll put this link in the cover letter or commit log for a reminder.

>
>> In the previous version, we added a "no_counter" bit to perf_event_attr, and
>> that will be exposed to user ABI, which seems not good.
>> (https://lkml.org/lkml/2019/2/14/791)
>> So we wrap a new kernel API above to support this.
>>
>> Do you have a different suggestion to do this?
>> (exclude host/guest just clears the enable bit when on VM-exit/entry,
>> still consumes the counter)
> Just add an argument to perf_event_create_kernel_counter() ?

Yes. I didn't find a proper place to add this "no_counter" indicator, so 
added a
wrapper to avoid changing existing callers of 
perf_event_create_kernel_counter.

Best,
Wei