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Thu, 12 Nov 2026 04:15:54 -0800 (PST) Received: from mi-ThinkCentre-M760t.mioffice.cn ([43.224.245.234]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-3752060dc0csm29740235eec.14.2026.11.12.04.15.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Nov 2026 04:15:54 -0800 (PST) From: Wenwu Hou To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Wenwu Hou Subject: [PATCH v2] tracing/hwlat: Do the latency calculations in nanoseconds Date: Thu, 12 Nov 2026 20:15:01 +0800 Message-ID: <20261112121502.2070755-1-hwenwur@gmail.com> X-Mailer: git-send-email 2.43.0 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-Transfer-Encoding: 8bit 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. Do all the latency calculations in nanoseconds instead, and only convert the durations to microseconds when recording the hwlat event. Fixes: e7c15cd8a1133 ("tracing: Added hardware latency tracer") Suggested-by: Steven Rostedt Signed-off-by: Wenwu Hou --- Tested in a 4-vCPU KVM guest; all three hwlat modes worked as expected. Changes in v2: - Perform the latency calculations in nanoseconds instead of converting only the maximum latency, as suggested by Steven Rostedt. - Convert the durations to microseconds only when recording the hwlat event to preserve the existing event format. kernel/trace/trace_hwlat.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c index 65e184d800ff1..a16905ac12b0d 100644 --- a/kernel/trace/trace_hwlat.c +++ b/kernel/trace/trace_hwlat.c @@ -203,14 +203,12 @@ static int get_sample(void) time_type start, t1, t2, last_t2; s64 diff, outer_diff, total, last_total = 0; u64 sample = 0; - u64 sample_width = READ_ONCE(hwlat_data.sample_width); + u64 sample_width = READ_ONCE(hwlat_data.sample_width) * NSEC_PER_USEC; u64 thresh = tracing_thresh; u64 outer_sample = 0; int ret = -1; unsigned int count = 0; - do_div(thresh, NSEC_PER_USEC); /* modifies interval value */ - kdata->nmi_total_ts = 0; kdata->nmi_count = 0; /* Make sure NMIs see this first */ @@ -229,7 +227,7 @@ static int get_sample(void) if (time_u64(last_t2)) { /* Check the delta from outer loop (t2 to next t1) */ - outer_diff = time_to_us(time_sub(t1, last_t2)); + outer_diff = time_sub(t1, last_t2); /* This shouldn't happen */ if (outer_diff < 0) { hwlat_err(BANNER "time running backwards\n"); @@ -240,7 +238,7 @@ static int get_sample(void) } last_t2 = t2; - total = time_to_us(time_sub(t2, start)); /* sample width */ + total = time_sub(t2, start); /* sample width */ /* Check for possible overflows */ if (total < last_total) { @@ -250,7 +248,7 @@ static int get_sample(void) last_total = total; /* This checks the inner loop (t1 to t2) */ - diff = time_to_us(time_sub(t2, t1)); /* current diff */ + diff = time_sub(t2, t1); /* current diff */ if (diff > thresh || outer_diff > thresh) { if (!count) @@ -286,8 +284,8 @@ static int get_sample(void) do_div(kdata->nmi_total_ts, NSEC_PER_USEC); s.seqnum = atomic64_inc_return(&hwlat_data.count); - s.duration = sample; - s.outer_duration = outer_sample; + s.duration = time_to_us(sample); + s.outer_duration = time_to_us(outer_sample); s.nmi_total_ts = kdata->nmi_total_ts; s.nmi_count = kdata->nmi_count; s.count = count; -- 2.43.0