From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 183D03F1AD3 for ; Wed, 19 Aug 2026 08:45:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787129121; cv=none; b=s1LBn69v+xLEBRTRYPtSEfnjt6UedGInuNXHUMTve41YJq9Z3zq243pyZxHARvOnmdwLXb7Bh1qaC6CbmCl4+M1ZVhOt3VO5XZKC1Tp2jJyOtZD3/4aTWuYy7eYbX51gSuP4qCFoD/SxgGr140LuZqipDsE30SUp7V/776T0EcY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787129121; c=relaxed/simple; bh=+aHPlIAKmlb/qA4aZRXFzfPHKV26rayOq1J+KtH4ivQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FUvd/KG62GMDAH3vaufnwBd8JGcDN3QVaNfbxWNYVpHGOF53XQ9E4WFVQ2m0NR7DFegE9iNEY317mr9bej40g0n/WN3I0JE8vVXhodxN2GrYYhtgkbcgbRwqpAUvuYvf6/E0BDBlWHeCb+O6BoK/1tnSZ5Hfq1Rai5JVUwKUZqE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=TZipHbMW; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="TZipHbMW" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0EFF4153B; Wed, 19 Aug 2026 01:45:14 -0700 (PDT) Received: from localhost (unknown [10.2.196.114]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8981C3F66F; Wed, 19 Aug 2026 01:45:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1787129118; bh=+aHPlIAKmlb/qA4aZRXFzfPHKV26rayOq1J+KtH4ivQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TZipHbMWLvpXTTZgT91Nhe/tCT/Q6bKzjQFFaEc464Re2lX5Jnfsq1RFMdIy5QSqv 2b8CxoPh03mEyHdYQ7M/3Z6cpSEuCQlu7GxNih6RI725ERT4NmOiR1v6Du+xMRDMiA g3wltJNirnKR7sjBRrAZT8wuHSAojxGDcP2qKifA= Date: Wed, 19 Aug 2026 09:45:15 +0100 From: Leo Yan To: James Clark Cc: Suzuki K Poulose , Mike Leach , Suyash Mahar , Yeoreum Yun , Greg Kroah-Hartman , Qi Liu , Junhao He , coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Jonathan Cameron Subject: Re: [PATCH v3 4/8] coresight: tmc-etr: Prevent per-thread events from sharing a sink Message-ID: <20260819084515.GF8904@e132581.arm.com> References: <20260728-james-cs-multiple-per-threads-v3-0-6aee7579f1dc@linaro.org> <20260728-james-cs-multiple-per-threads-v3-4-6aee7579f1dc@linaro.org> <20260813160504.GC8904@e132581.arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Aug 14, 2026 at 10:09:01AM +0100, James Clark wrote: [...] > There isn't any sharing with "another perf session", unless there is a > mistake somewhere? Checking that the owners are equivalent enforces this. Or > do you mean another event owned by the same process? Now I understand that the problem is constrained to different events within the same session. > I'm not sure the exact model you had in mind was that still supports this > and fixes the bugs? Let me try to describe my understanding of the problem. ./perf test -w named_threads 2 1000000 & ./perf record -e cs_etm//u --per-thread --pid $! We can simplify the flow as: | T1 | CPU0 ------------------------------ | T2 | CPU1 ------------------------------ `> T2 stops and the driver reports the warning when trying to sync ETR_BUF(T1), while T2 is associated with ETR_BUF(T2). AUX_BUF(T1) | | ETR_BUF(T1) | Bounce buf0 | -> Used by H/W trace AUX_BUF(T2) | | ETR_BUF(T2) | Bounce buf1 | -> Not used by H/W trace With `--per-thread --pid $PID`, perf creates separate events for the child threads, say T1 and T2. Perf allocates a separate AUX buffer for each event, and the ETR driver also allocates a separate bounce buffer for each event. However, because there is only one shared ETR sink, only one of those bounce buffers can actually be used by the hardware at a time. If T1 stops while T2 is still running, the ETR remains enabled. Later, when T2 stops, the ETR is still using ETR_BUF(T1). This mismatch triggers the warning and prevents the data from being copied. I am just wandering if we can improve the sink driver to only allocate a single bounce buffer that is independent of any threads (and any associated events). | T1 | CPU0 ------------------------------ | T2 | CPU1 ------------------------------ `> T2 stops and can sync trace from the shared bounce buffer to AUX_BUF(T2). AUX_BUF(T1) | | AUX_BUF(T2) | | ETR_BUF | Bounce buf | -> Used by H/W trace This might also simplify the CPU-wide case. Each CPU would still have its own AUX buffer, but the ETR driver would maintain only one bounce buffer for the shared sink. A reference count could track how many events are using the sink, with the final event responsible for stopping the sink and copying the trace data from bounce buffer to aux buffer. > The one in this change is pretty complete and only does 4 comparisons, > which seems quite simple to me. Before going further with the heavily sink buffer refactoring, perhaps a more pragmatic solution would be to reject the problematic case for now. Can we do something like below? +void coresight_trace_id_is_perf_started(struct coresight_trace_id_map *id_map) +{ + PERF_SESSION(atomic_read(&id_map->perf_cs_etm_session_active)); +} @@ -399,6 +399,15 @@ etm_event_build_path(struct perf_event *event, int cpu, goto out; } + if (!coresight_trace_id_is_perf_started(&sink->perf_sink_id_map)) { + sink->perf_owner = event->owner; + sink->perf_target = event->hw.target; + } else { + if (sink->perf_owner != event->owner || + sink->perf_target != event->hw.target) + goto out; + } + We use a central place etm_event_build_path() to record and compare event's owner and target process, then we don't need to spread the check into sink drivers. We only care about if owner and target must be consistent. Regard of the inherit/inherit_thread, I always see they are consistent within the same session. Should we ignore them? Thanks, Leo