linux-kernel - [PATCH 1/3] tracing/timerlat: Notify IRQ new max latency only if stop tracing is set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <2c2d9a56c0886c8402ba320de32856cbbb10c2bb.1652175637.git.bristot@kernel.org>
Date:   Tue, 10 May 2022 11:45:23 +0200
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
        linux-trace-devel@...r.kernel.org
Cc:     Daniel Bristot de Oliveira <bristot@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Clark Williams <williams@...hat.com>
Subject: [PATCH 1/3] tracing/timerlat: Notify IRQ new max latency only if stop tracing is set

Currently, the notification of a new max latency is sent from
timerlat's IRQ handler anytime a new max latency is found.

While this behavior is not wrong, the send IPI overhead itself
will increase the thread latency and that is not the desired
effect (tracing overhead).

Moreover, the thread will notify a new max latency again because
the thread latency as it is always higher than the IRQ latency
that woke it up.

The only case in which it is helpful to notify a new max latency
from IRQ is when stop tracing (for the IRQ) is set, as in this
case, the thread will not be dispatched.

Notify a new max latency from the IRQ handler only if stop tracing is
set for the IRQ handler.

Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Reported-by: Clark Williams <williams@...hat.com>
Fixes: a955d7eac177 ("trace: Add timerlat tracer")
Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
---
 kernel/trace/trace_osnoise.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index e9ae1f33a7f0..6494ca27ea6f 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1578,11 +1578,12 @@ static enum hrtimer_restart timerlat_irq(struct hrtimer *timer)
 
 	trace_timerlat_sample(&s);
 
-	notify_new_max_latency(diff);
-
-	if (osnoise_data.stop_tracing)
-		if (time_to_us(diff) >= osnoise_data.stop_tracing)
+	if (osnoise_data.stop_tracing) {
+		if (time_to_us(diff) >= osnoise_data.stop_tracing) {
 			osnoise_stop_tracing();
+			notify_new_max_latency(diff);
+		}
+	}
 
 	wake_up_process(tlat->kthread);
 
-- 
2.32.0