From patchwork Sun Aug 18 13:18:24 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Masami Hiramatsu (Google)" X-Patchwork-Id: 13767442 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CE5CC22087; Sun, 18 Aug 2024 13:18:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723987108; cv=none; b=Soj5JQWm5LQ8eJBSgO0J0KEXhilcFXr6mgFcegWz5f59qS+RMI3zFTeHcJ1Cl52U/W2ioEKCr5dlXQUPi0ACMvUub3nolKbpdEQx53BDN6238BVLXv568bPoKMKL+5VhklTuLREYmjByKF4FViY5P5+G+0xf0ff00SFd1cusrjc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723987108; c=relaxed/simple; bh=hLcYh/8kfLYaxmwpE9Cu4m98j4Ls5BtM9m3SN1sODwU=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=bcKWv+Em3a0YLUw4KC6ESjbaGujQ1sOpBf1gcybppAvVG+PWQm+nspWNq7MHooP9WhYmf1SO6LLNAwe4MUkssVuaS197v0FfL8DXG2LJS3VfVJNJQVKEsnFvS17jhszjKfGbWca2TL5vd5eJqcbLn9P0Em+wwQgm1Lo23comeGs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i++ckh7g; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="i++ckh7g" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D80BC32786; Sun, 18 Aug 2024 13:18:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723987108; bh=hLcYh/8kfLYaxmwpE9Cu4m98j4Ls5BtM9m3SN1sODwU=; h=From:To:Cc:Subject:Date:From; b=i++ckh7g57lWb67dS5w9G94lYcEQoa0g7ts3QheBtVIBiQuq5fN8TQd8JoY6imw2s Og1oKOdpFVWWBrpasGN5ftc4ifZbVkNwdEUXilO18OmmzW+rY6JX0UsIiATxiknu8h 7f1/ZOgUhgtKlDeD7Uei7i0TdBw5x8VCyYKm//S4JJWCF5zr/4ygJEfEXqe3ZU1Zi4 JNStbJdmmJnlLLWx28ACEIPctVV9sNLJ2oUDv5u9eqp9/iXp4ybbkxp4+ELo6YZA71 spF5VkZg5oExOAHOoqHo9g6Yy19RnJU6sv6l898w2Zaxq3BufcGKAEsO7/66Pzrv6G Evq8YWqserVqg== From: "Masami Hiramatsu (Google)" To: Steven Rostedt , Shuah Khan Cc: Masami Hiramatsu , Tom Zanussi , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v5 0/3] tracing: Support poll on event hist file Date: Sun, 18 Aug 2024 22:18:24 +0900 Message-Id: <172398710447.295714.4489282566285719918.stgit@devnote2> X-Mailer: git-send-email 2.34.1 User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Hi, Here is the v5 patch to support polling on event 'hist' file. The previous version is here; https://lore.kernel.org/all/172377544331.67914.7474878424159759789.stgit@devnote2/ This version just update the comment in poll.c and add Shuah's Reviewed-by. Background ---------- There has been interest in allowing user programs to monitor kernel events in real time. Ftrace provides `trace_pipe` interface to wait on events in the ring buffer, but it is needed to wait until filling up a page with events in the ring buffer. We can also peek the `trace` file periodically, but that is inefficient way to monitor a randomely happening event. Overview -------- This patch set allows user to `poll`(or `select`, `epoll`) on event histogram interface. As you know each event has its own `hist` file which shows histograms generated by trigger action. So user can set a new hist trigger on any event you want to monitor, and poll on the `hist` file until it is updated. There are 2 poll events are supported, POLLIN and POLLPRI. POLLIN means that there are any readable update on `hist` file and this event will be flashed only when you call read(). So, this is useful if you want to read the histogram periodically. The other POLLPRI event is for monitoring trace event. Like the POLLIN, this will be returned when the histogram is updated, but you don't need to read() the file and use poll() again. Note that this waits for histogram update (not event arrival), thus you must set a histogram on the event at first. Usage ----- Here is an example usage: ---- TRACEFS=/sys/kernel/tracing EVENT=$TRACEFS/events/sched/sched_process_free # setup histogram trigger and enable event echo "hist:key=comm" >> $EVENT/trigger echo 1 > $EVENT/enable # Wait for update poll pri $EVENT/hist # Event arrived. echo "process free event is comming" tail $TRACEFS/trace ---- The 'poll' command is in the selftest patch. You can take this series also from here; https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/log/?h=topic/event-hist-poll Thank you, --- Masami Hiramatsu (Google) (3): tracing/hist: Add poll(POLLIN) support on hist file tracing/hist: Support POLLPRI event for poll on histogram selftests/tracing: Add hist poll() support test include/linux/trace_events.h | 5 + kernel/trace/trace_events.c | 18 ++++ kernel/trace/trace_events_hist.c | 101 +++++++++++++++++++- tools/testing/selftests/ftrace/Makefile | 2 tools/testing/selftests/ftrace/poll.c | 74 +++++++++++++++ .../ftrace/test.d/trigger/trigger-hist-poll.tc | 74 +++++++++++++++ 6 files changed, 271 insertions(+), 3 deletions(-) create mode 100644 tools/testing/selftests/ftrace/poll.c create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc -- Masami Hiramatsu (Google)