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dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=goodmis.org header.i=@goodmis.org header.a=rsa-sha256 header.s=dkim1 header.b=q0TPU5yP Received: from omf03.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id C61571A055D; Thu, 12 Nov 2026 10:13:10 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf03.hostedemail.com (Postfix) with ESMTPA id 14D266000F; Thu, 12 Nov 2026 10:13:03 +0000 (UTC) Date: Thu, 12 Nov 2026 05:12:49 -0500 From: Steven Rostedt To: Wenwu Hou Cc: mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] tracing/hwlat: Store the maximum latency in nanoseconds Message-ID: <20261112051249.7c19f22e@fedora> In-Reply-To: <20261111031304.1442318-1-hwenwur@gmail.com> References: <20261111031304.1442318-1-hwenwur@gmail.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 4fy5uz88u5rz8yxckudtndmo5esdexp6 X-Rspamd-Server: rspamout04 X-Rspamd-Queue-Id: 14D266000F X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX198Fmx32fbNpCc2swGmT014WFRtB7xiuzE= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=2BmWYKOiyjIsi4QXb/VAu1SFL4RNR0NUHUQfqyXSb28=; b=q0TPU5yPLZ947aX3Sv3isuOYZBA7m2KqP762P/02ChGLc6vvPi3+qhkwOX7XLjBCSH1wp2Wxihf264VSdeWIX1XHdIsIqWoH5B3Bww0FFqONTl5WPZWRLDRi61cw/bwR1zvdWYxJACh5iXbWtX0OcK2qlavTYf6dXp1CiJ/GPGY= X-HE-Tag: 1794478383-904335 X-HE-Meta: U2FsdGVkX1+Afnel4CygBPUzz6ifRPiBAp2WGZmEnf5aajhccC3buV9ITyD0sRbT2qBarctUj7GMLNH0pEmdUy8M+YF7/AFduefpXVF7Ngd7ytBKF7XnY7lg5vBy1Nq9F2MRpa5MaOS1dEKhekwfqoyQkudIJfTU27ify8xrU6sU2FcgXP+fC4t03pLcfcIaTi1URKGjlcAfy54/3Mos5uL+ZofYT0kAc3pzP9gjt/2wqMGOQbaEumEtNyGEOAZWVP5MYQY3lnFhuQqYf64D/K/Z7XsItUMKLw1SmSVdVT7rU05CVvZt4e/Y4uyDFVBOKvu7XsoOESQZeLdyIRb72EugCaEQY9ag On Wed, 11 Nov 2026 11:13:04 +0800 Wenwu Hou wrote: > tr->max_latency is expected to hold nanoseconds: tracing_max_lat_read() > converts it with nsecs_to_usecs() to print the usecs documented in > hwlat_detector.rst, and the other latency tracers store nanoseconds there > too. > > Fixes: e7c15cd8a1133 ("tracing: Added hardware latency tracer") > Signed-off-by: Wenwu Hou Amazing that this bug has been here for 10 years and nobody noticed. > --- > kernel/trace/trace_hwlat.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c > index 65e184d800ff1..701b6a542e51a 100644 > --- a/kernel/trace/trace_hwlat.c > +++ b/kernel/trace/trace_hwlat.c > @@ -293,7 +293,7 @@ static int get_sample(void) > s.count = count; > trace_hwlat_sample(&s); > > - latency = max(sample, outer_sample); > + latency = max(sample, outer_sample) * NSEC_PER_USEC; The real fix is to just use nanoseconds in the calculations. The only reason it was doing the conversions was to match max_latency anyway. The time recorded in the events would need to be converted to microseconds too, if the raw numbers are in nanos. Thanks, -- Steve > > /* Keep a running maximum ever recorded hardware latency */ > if (latency > tr->max_latency) {