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Date: Thu, 19 Dec 2024 11:04:34 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>, Tom Zanussi <zanussi@kernel.org>, Mathieu
 Desnoyers <mathieu.desnoyers@efficios.com>, linux-kernel@vger.kernel.org,
 linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v6 3/3] selftests/tracing: Add hist poll() support test
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In-Reply-To: <172907578159.470540.12276069200453397317.stgit@mhiramat.roam.corp.google.com>
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On Wed, 16 Oct 2024 19:49:41 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc
> @@ -0,0 +1,74 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +# description: event trigger - test poll wait on histogram
> +# requires: set_event events/sched/sched_process_free/trigger events/sched/sched_process_free/hist
> +# flags: instance
> +
> +POLL=${FTRACETEST_ROOT}/poll
> +
> +if [ ! -x ${POLL} ]; then
> +  echo "poll program is not compiled!"
> +  exit_unresolved
> +fi
> +
> +EVENT=events/sched/sched_process_free/
> +
> +# Check poll ops is supported. Before implementing poll on hist file, it
> +# returns soon with POLLIN | POLLOUT, but not POLLPRI.
> +
> +# This must wait >1 sec and return 1 (timeout).
> +set +e
> +${POLL} -I -t 1000 ${EVENT}/hist
> +ret=$?
> +set -e
> +if [ ${ret} != 1 ]; then
> +  echo "poll on hist file is not supported"
> +  exit_unsupported
> +fi
> +
> +# Test POLLIN
> +echo > trace
> +echo "hist:key=comm" > ${EVENT}/trigger
> +echo 1 > ${EVENT}/enable
> +
> +# This sleep command will exit after 2 seconds.
> +sleep 2 &
> +BGPID=$!
> +# if timeout happens, poll returns 1.
> +${POLL} -I -t 4000 ${EVENT}/hist
> +echo 0 > tracing_on
> +
> +if [ -d /proc/${BGPID} ]; then
> +  echo "poll exits too soon"
> +  kill -KILL ${BGPID} ||:
> +  exit_fail
> +fi
> +
> +if ! grep -qw "sleep" trace; then
> +  echo "poll exits before event happens"

I ran this and it failed here. But it wasn't because the poll failed, it's
because the test is wrong. If something else exits during the test, then
the poll function will exit early.

What the check should do is simply read the hist file, get the hist count,
and make sure it's updated after the poll is run, or at least put a filter
on it:

  echo 'hist:keys=comm if comm =="sleep"' > /sys/kernel/tracing/events/sched/sched_process_free/trigger

Which would work as long as no other "sleep" exits during the test.

-- Steve

> +  exit_fail
> +fi
> +
> +# Test POLLPRI
> +echo > trace
> +echo 1 > tracing_on
> +
> +# This sleep command will exit after 2 seconds.
> +sleep 2 &
> +BGPID=$!
> +# if timeout happens, poll returns 1.
> +${POLL} -P -t 4000 ${EVENT}/hist
> +echo 0 > tracing_on
> +
> +if [ -d /proc/${BGPID} ]; then
> +  echo "poll exits too soon"
> +  kill -KILL ${BGPID} ||:
> +  exit_fail
> +fi
> +
> +if ! grep -qw "sleep" trace; then
> +  echo "poll exits before event happens"
> +  exit_fail
> +fi
> +
> +exit_pass