Re: [PATCH v2 0/3] perf-stat: share hardware PMCs with BPF

[Song Liu <songliubraving@fb.com>]

> On Mar 19, 2021, at 8:58 AM, Namhyung Kim <namhyung@kernel.org> wrote:
> 
> Hi Arnaldo,
> 
> On Sat, Mar 20, 2021 at 12:35 AM Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
>> 
>> Em Fri, Mar 19, 2021 at 09:54:59AM +0900, Namhyung Kim escreveu:
>>> On Fri, Mar 19, 2021 at 9:22 AM Song Liu <songliubraving@fb.com> wrote:
>>>>> On Mar 18, 2021, at 5:09 PM, Arnaldo <arnaldo.melo@gmail.com> wrote:
>>>>> On March 18, 2021 6:14:34 PM GMT-03:00, Jiri Olsa <jolsa@redhat.com> wrote:
>>>>>> On Thu, Mar 18, 2021 at 03:52:51AM +0000, Song Liu wrote:
>>>>>>> perf stat -C 1,3,5                  107.063 [sec]
>>>>>>> perf stat -C 1,3,5 --bpf-counters   106.406 [sec]
>> 
>>>>>> I can't see why it's actualy faster than normal perf ;-)
>>>>>> would be worth to find out
>> 
>>>>> Isn't this all about contended cases?
>> 
>>>> Yeah, the normal perf is doing time multiplexing; while --bpf-counters
>>>> doesn't need it.
>> 
>>> Yep, so for uncontended cases, normal perf should be the same as the
>>> baseline (faster than the bperf).  But for contended cases, the bperf
>>> works faster.
>> 
>> The difference should be small enough that for people that use this in a
>> machine where contention happens most of the time, setting a
>> ~/.perfconfig to use it by default should be advantageous, i.e. no need
>> to use --bpf-counters on the command line all the time.
>> 
>> So, Namhyung, can I take that as an Acked-by or a Reviewed-by? I'll take
>> a look again now but I want to have this merged on perf/core so that I
>> can work on a new BPF SKEL to use this:
> 
> I have a concern for the per cpu target, but it can be done later, so
> 
> Acked-by: Namhyung Kim <namhyung@kernel.org>
> 
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.bpf/bpf_perf_enable
> 
> Interesting!  Actually I was thinking about the similar too. :)

Hi Namhyung, Jiri, and Arnaldo,

Thanks a lot for your kind review. 

Here is updated 3/3, where we use perf-bench instead of stressapptest.

Thanks,
Song


From cc79d161be9c9d24198f7e35b50058a6e15076fd Mon Sep 17 00:00:00 2001
From: Song Liu <songliubraving@fb.com>
Date: Tue, 16 Mar 2021 00:19:53 -0700
Subject: [PATCH v3 3/3] perf-test: add a test for perf-stat --bpf-counters
 option

Add a test to compare the output of perf-stat with and without option
--bpf-counters. If the difference is more than 10%, the test is considered
as failed.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 tools/perf/tests/shell/stat_bpf_counters.sh | 31 +++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100755 tools/perf/tests/shell/stat_bpf_counters.sh

diff --git a/tools/perf/tests/shell/stat_bpf_counters.sh b/tools/perf/tests/shell/stat_bpf_counters.sh
new file mode 100755
index 0000000000000..7aabf177ce8d1
--- /dev/null
+++ b/tools/perf/tests/shell/stat_bpf_counters.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+# perf stat --bpf-counters test
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+
+# check whether $2 is within +/- 10% of $1
+compare_number()
+{
+       first_num=$1
+       second_num=$2
+
+       # upper bound is first_num * 110%
+       upper=$(( $first_num + $first_num / 10 ))
+       # lower bound is first_num * 90%
+       lower=$(( $first_num - $first_num / 10 ))
+
+       if [ $second_num -gt $upper ] || [ $second_num -lt $lower ]; then
+               echo "The difference between $first_num and $second_num are greater than 10%."
+               exit 1
+       fi
+}
+
+# skip if --bpf-counters is not supported
+perf stat --bpf-counters true > /dev/null 2>&1 || exit 2
+
+base_cycles=$(perf stat --no-big-num -e cycles -- perf bench sched messaging -g 1 -l 100 -t 2>&1 | awk '/cycles/ {print $1}')
+bpf_cycles=$(perf stat --no-big-num --bpf-counters -e cycles -- perf bench sched messaging -g 1 -l 100 -t 2>&1 | awk '/cycles/ {print $1}')
+
+compare_number $base_cycles $bpf_cycles
+exit 0
--
2.30.2