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Wed, 12 Nov 2025 01:21:31 -0800 (PST) Message-ID: <9008f2e6-d2de-4765-b824-cdd6a1175794@linaro.org> Date: Wed, 12 Nov 2025 09:21:28 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 0/5] Remove NO_AUXTRACE build option To: Ian Rogers , Namhyung Kim Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Adrian Hunter , John Garry , Will Deacon , Mike Leach , Leo Yan , Suzuki K Poulose , Yicong Yang , Jonathan Cameron , Thomas Gleixner , Darren Hart , Davidlohr Bueso , =?UTF-8?Q?Andr=C3=A9_Almeida?= , Tomas Glozar , Quentin Monnet , Yuzhuo Jing , Blake Jones , Charlie Jenkins , Yeoreum Yun , Athira Rajeev , Ravi Bangoria , Collin Funk , Dapeng Mi , Thomas Richter , Dmitry Vyukov , Andi Kleen , Howard Chu , Zecheng Li , tanze , Gabriele Monaco , GuoHan Zhao , Markus Elfring , Colin Ian King , Kan Liang , "Dr. David Alan Gilbert" , Jean-Philippe Romain , Yang Li , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org References: <20251110013152.3099080-1-irogers@google.com> Content-Language: en-US From: James Clark In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/11/2025 6:01 pm, Ian Rogers wrote: > On Mon, Nov 10, 2025 at 10:21 PM Namhyung Kim wrote: >> >> Hi Ian, >> >> On Sun, Nov 09, 2025 at 05:31:47PM -0800, Ian Rogers wrote: >>> Switch the __get_cpuid feature for intel-pt to use the provided cpuid >>> function in perf, this removes the need for NO_AUXTRACE when the >>> feature detection fails. Remove the now unnecessary feature >>> detection. Remove NO_AUXTRACE as it just builds a more broken version >> >> Can you please elaborate what the broken part is? > > Sure. I'll summarize what alters in patch 4. NO_AUXTRACE is > controlling 3 main things: > * set up of aux options for PMUs (code in the arch directory) > * ARM: coresight and SPE > * Intel: BTS and PT > * PowerPC: VPA DTL > * S390: cpumsf > * support for decoding aux events (common code that can be > cross-compiled assuming other library dependencies are available) > * ARM: coresight > * HiSi: PTT decoder > * Intel: BTS and PT > * PowerPC: VPA DTL > * S390: cpumsf > * Tool support for aux buffers (common shared builtin code): > * perf record: aux options for events, snapshot, aux-sample > * perf inject: aux events will fail the entire perf inject command > > So somebody with a NO_AUXTRACE build would generally experience a very > sad perf command. Having the option made sense when there were feature > tests that could fail, but possibly that should have just controlled > not compiling intel-pt. Having the option is extra burden on > developers/maintainers, as shown in my comment: > >> This was prompted by needing to make a v2 patch set of: >> https://lore.kernel.org/lkml/20251107170712.2302714-1-irogers@google.com/ >> due to a broken NO_AUXTRACE configuration. > > Somebody may have been using NO_AUXTRACE as a proxy for not having > some library, but I don't see that in the code. If this is the case we > should add the appropriate feature test, .. > Not having NO_AUXTRACE may have been a bug work around for someone, in > which case we should work to fix the bug. Again, I don't know of this > case and don't see it in the code. > > Thanks, > Ian > >> Thanks, >> Namhyung Seems like a nice simplification even if nothing was badly broken. Reviewed-by: James Clark