Message-ID: <838392a5-0b60-4b43-6d5f-b97524f6f157@amd.com>
Date:   Mon, 13 Mar 2023 21:10:36 +0530
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Subject: Re: [PATCH v2 2/3] perf/ibs: Fix interface via core pmu events
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     namhyung@kernel.org, eranian@google.com, acme@kernel.org,
        mark.rutland@arm.com, jolsa@kernel.org, irogers@google.com,
        bp@alien8.de, x86@kernel.org, linux-perf-users@vger.kernel.org,
        linux-kernel@vger.kernel.org, sandipan.das@amd.com,
        ananth.narayan@amd.com, santosh.shukla@amd.com,
        Ravi Bangoria <ravi.bangoria@amd.com>
References: <20230309101111.444-1-ravi.bangoria@amd.com>
 <20230309101111.444-3-ravi.bangoria@amd.com>
 <20230312145426.GA1757905@hirez.programming.kicks-ass.net>
 <45de7e62-d951-1019-990e-6df285a64cf6@amd.com>
 <20230313142156.GL2017917@hirez.programming.kicks-ass.net>
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From:   Ravi Bangoria <ravi.bangoria@amd.com>
In-Reply-To: <20230313142156.GL2017917@hirez.programming.kicks-ass.net>
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On 13-Mar-23 7:51 PM, Peter Zijlstra wrote:
> On Mon, Mar 13, 2023 at 05:59:46PM +0530, Ravi Bangoria wrote:
> 
>>> Now, we already have a gruesome hack in there, and I'm thikning you
>>> should use that instead of adding yet another one. Note:
>>>
>>> 		if (ret == -ENOENT && event->attr.type != type && !extended_type) {
>>> 			type = event->attr.type;
>>> 			goto again;
>>>
>>> So if you have amd_pmu_hw_config() do:
>>>
>>> 	event->attr.type = ibs_pmu.type;
>>> 	return -ENOENT;
>>>
>>> it should all just work no?
>>
>> IBS driver needs to convert RAW pmu config to IBS config, which it does
>> based on original event->attr.type. See perf_ibs_precise_event(). This
>> logic will fail with event->attr.type overwrite.
> 
> amd_pmu_hw_config() could also rewrite event->attr.config I suppose.

This might work. Let me try.

> 
> I don't think we actually use/expose these event->attr fields again
> after all this, do wel?

I'll confirm this as well.

> 
> The closest to that is perf_event_modify_attr(), but that is limited to
> TYPE_BREAKPOINT for the time being (also, could this be used to cure
> your in-kernel IBS usage woes?).

I think doing it transparently at the arch layer would be better.

Thanks,
Ravi