From patchwork Tue Jun 25 15:16:52 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: 13711575 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 13038172786; Tue, 25 Jun 2024 15:16:56 +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=1719328617; cv=none; b=pP+Bd6jenSqgGPBDLeuHJYaTBYrP04VKXZ4J/POEhCeooEz1eSpMepU3GFgQFZn/NDK3xwUoLoZS4EAYIdATeQIdsoTnLuzTLqD4u1jaCesFkbC2CZEIkUWhk5H3ITyTg7h5PczacoNxRXlpAQCXRkwNdT9Ecn5zR7Y6xm7s6y0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719328617; c=relaxed/simple; bh=UGARZKPk5YbSS64uqg+buewtBHJklTJcopEoDSowNjE=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=A7EMXIJ2KbfHBVhJUClbUlz8twgYRbtD8sfOvEo90jcnD0wvZgC/xn/uYvXGbOqUya571TtUH7NCbH9cQdCmcybKvZ7y32Box9qIKVDEZz+8eZC3XkvYeJpfF7WELQolxB0quVdkCejJcimLS216mjTXgUo8aaJHeUcbKKNWh+0= 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/6F6zkq; 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/6F6zkq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD93CC32782; Tue, 25 Jun 2024 15:16:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719328616; bh=UGARZKPk5YbSS64uqg+buewtBHJklTJcopEoDSowNjE=; h=From:To:Cc:Subject:Date:From; b=I/6F6zkqfPrNZhs98ids3A35JkyaGhxXPESrV47EWlxg8lubv1i1ikKbv7ZcmIIRN DHqOnxP9lWH2qJiukw0h60yG26/nkwWpZ9xHXcR0laNvIqCZamDB/c6ASiN/PMBZ2z k+D68My8uIpi8DelGI8G7wz4DSXtzB0wzLLXMsvCnn9gopflH5K+f5qTSnsPTl/x8B oDsL58ubMwlbj6Ig6DKMHohxpndDAJE0E3XC9Xni3Pbs8jqoEkcMsKNdQdzZuGHNHX qCcOqiWFT8ENbMUhMSZDJZOIL20kvlQNTVNmAdhyCfebkuvWTQvIwTfvhb//IfK3KH 1bSSr1unBGvXA== 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: [RFC PATCH 0/3] tracing: Support poll on event hist file Date: Wed, 26 Jun 2024 00:16:52 +0900 Message-Id: <171932861260.584123.15653284949837094747.stgit@devnote2> X-Mailer: git-send-email 2.34.1 User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Hi, Here is an RFC patch to support polling on event 'hist' file. 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. 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. 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 $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, Reviewed-by: Tom Zanussi --- 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 | 3 + tools/testing/selftests/ftrace/poll.c | 34 +++++++ .../ftrace/test.d/trigger/trigger-hist-poll.tc | 46 +++++++++ 6 files changed, 204 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)