Date:   Mon, 13 Mar 2023 15:21:56 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ravi Bangoria <ravi.bangoria@amd.com>
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
Subject: Re: [PATCH v2 2/3] perf/ibs: Fix interface via core pmu events
Message-ID: <20230313142156.GL2017917@hirez.programming.kicks-ass.net>
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>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <45de7e62-d951-1019-990e-6df285a64cf6@amd.com>
Precedence: bulk

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.

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

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?).