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Date: Wed, 4 Aug 2021 09:23:39 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Ahmed S. Darwish" <a.darwish@...utronix.de>
Cc: linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
Tom Zanussi <zanussi@...nel.org>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
linux-rt-users <linux-rt-users@...r.kernel.org>,
Clark Williams <williams@...hat.com>
Subject: Re: [PATCH v2 00/21] libtracefs: Introducing tracefs_sql() to
create synthetice events with an SQL line
On Wed, 4 Aug 2021 13:57:00 +0200
"Ahmed S. Darwish" <a.darwish@...utronix.de> wrote:
> Thanks a lot! Actually, I meant going even one step further ;)
>
> I was imagining something like the following:
>
> $ trace-cmd sql-shell # OR
>
> $ perf tracefs-sql-shell
>
> Welcome to tracefs SQL shell...
>
> > SELECT PNAME(common_pid),msr,val
> FROM write_msr
> WHERE msr=72 OR msr=2096
>
> .-------------------------------------------.
> | PNAME(common_pid) | msr | val |
> |---------------------|------ |-------------|
> | qemu-system-x86 | 0x48 | 0 |
> | qemu-system-x86 | 0x48 | 0 |
> | qemu-system-x86 | 0x48 | 0 |
> | kworker/u16:2 | 0x830 | 0x1000008fb |
> | .... | .... | ..... |
> +-------------------------------------------+
Well, the above looks more like a normal trace just being processed
differently. If you want that, I already have this:
https://lore.kernel.org/linux-trace-devel/20200116104804.5d2f71e2@gandalf.local.home/
Which I created to test the idea of using SQL to create synthetic events.
It simply converts the events in a trace.dat file into a sql format
file that can be used to read into a SQL database. As the patch shows:
$ trace-cmd sqldump > dump
$ mysql events < dump
MariaDB [events]> show tables;
+-----------------------------+
| Tables_in_events |
+-----------------------------+
| sched_migrate_task |
| sched_move_numa |
| sched_process_exec |
| sched_process_exit |
| sched_stat_runtime |
| sched_switch |
| sched_wake_idle_without_ipi |
| sched_wakeup |
| sched_waking |
+-----------------------------+
9 rows in set (0.001 sec)
MariaDB [events]> select * from sched_move_numa;
+-------------------+-------------+--------------+----------------------+------------+-------+-------+-------+---------+---------+---------+---------+
| common_timestamp | common_type | common_flags | common_preempt_count | common_pid | pid | tgid | ngid | src_cpu | src_nid | dst_cpu | dst_nid |
+-------------------+-------------+--------------+----------------------+------------+-------+-------+-------+---------+---------+---------+---------+
| 14943901721165973 | 305 | 0 | 0 | 27451 | 27451 | 27451 | 27451 | 5 | 1 | 22 | 0 |
| 14943901722548756 | 305 | 0 | 0 | 3684 | 3684 | 3684 | 3684 | 23 | 1 | 22 | 0 |
| 14943901779987828 | 305 | 0 | 0 | 13693 | 13693 | 13677 | 13693 | 7 | 1 | 22 | 0 |
+-------------------+-------------+--------------+----------------------+------------+-------+-------+-------+---------+---------+---------+---------+
3 rows in set (0.001 sec)
I never applied the patch, but perhaps you would be interested in this?
>
> > SELECT MAX(end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) AS MaxSystemLatency_us,
> PNAME(common_pid)
> FROM sched_waking AS start JOIN sched_switch AS end
> ON start.pid = stop.next_pid
Now the above would require parsing the histogram data, which is next
on our agenda. There's two routes we can take with this:
1) Add a "hist_raw" that shows the raw data from the kernel's
histogram table. It would still be in ASCII, but will be formatted for
machine readability and not for humans (like /proc/$$/stat vs /proc/$$/status)
2) We write another bison parser to parse the current format of the
histogram output, which looks like this:
# sqlhist -n lat -e 'SELECT end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as lat
FROM sched_waking as start JOIN sched_switch as end ON start.pid = end.next_pid'
# trace-cmd start -e lat -R 'hist:keys=common_pid.execname,lat:sort=lat'
# cat /sys/kernel/tracing/events/synthetic/lat/hist
# event histogram
#
# trigger info: hist:keys=common_pid.execname,lat:vals=hitcount:sort=lat:size=2048 [active]
#
{ common_pid: <idle> [ 0], lat: 2 } hitcount: 9
{ common_pid: <idle> [ 0], lat: 3 } hitcount: 3
{ common_pid: kworker/0:0 [ 10041], lat: 3 } hitcount: 7
{ common_pid: kworker/0:0 [ 10041], lat: 4 } hitcount: 5
{ common_pid: <idle> [ 0], lat: 4 } hitcount: 2
{ common_pid: <idle> [ 0], lat: 5 } hitcount: 9
{ common_pid: kworker/0:0 [ 10041], lat: 5 } hitcount: 14
{ common_pid: kworker/0:0 [ 10041], lat: 6 } hitcount: 5
{ common_pid: <idle> [ 0], lat: 6 } hitcount: 16
{ common_pid: <idle> [ 0], lat: 7 } hitcount: 19
[..]
{ common_pid: JS Helper [ 1366], lat: 96 } hitcount: 1
{ common_pid: <idle> [ 0], lat: 97 } hitcount: 1
{ common_pid: <idle> [ 0], lat: 99 } hitcount: 1
{ common_pid: <idle> [ 0], lat: 107 } hitcount: 1
{ common_pid: <idle> [ 0], lat: 108 } hitcount: 3
{ common_pid: <idle> [ 0], lat: 117 } hitcount: 1
{ common_pid: <idle> [ 0], lat: 118 } hitcount: 1
{ common_pid: sendmail [ 1739], lat: 130 } hitcount: 1
Totals:
Hits: 2212
Entries: 130
Dropped: 0
That file is a user space API, and we can write up another bison parser
to parse out the data.
Between the two approaches, #1 is probably the better way, but that
requires a kernel change, and the feature will not be available in
older kernels, and not available until we actually implement it.
Approach #2 can be done today and will work for older kernels too. Also,
if we do #2, it doesn't mean we can't still do #1.
>
> .-------------------------------------------.
> | MaxSystemLatency_us | PNAME(common_pid) |
> |---------------------|---------------------|
> | 350 | cyclictest |
> +-------------------------------------------+
>
> > SELECT (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) AS latency,
> PNAME(common_pid), PRIO(common_pid)
> FROM sched_waking AS start JOIN sched_switch AS end
> ON start.pid = stop.next_pid
> ORDER BY latency DESC
> LIMIT 5
>
> .----------------------------------------------------------.
> | Latency | PNAME(common_pid) | PRIO(common_pid) |
> |---------|-----------------------------|------------------|
> | 829 | cyclictest | SCHED_FIFO:98 |
> | 400 | cyclictest | SCHED_FIFO:98 |
> | 192 | pulseaudio-rt | SCHED_RR:48 |
> | 30 | firefox | SCHED_OTHER:0:0 |
> | 10 | kworker/0:0H-events_highpri | SCHED_OTHER:0:-20|
> +----------------------------------------------------------+
>
> > SELECT (end.TIMESTAMP_USECS - start.TIMESTAMP_USECS) as MaxIRQLatency_us
> FROM irq_disable as start JOIN irq_enable as end
> ON start.common_pid = end.common_pid,
> start.parent_offs == end.parent_offs
> ORDER BY max_irq_disable
> LIMIT 1
>
> .------------------.
> | MaxIRQLatency_us |
> |------------------|
> | 37 |
> +------------------+
>
> And so on....
>
> The idea was that since the community already picked SQL as a
> higher-level tracing language, why hard-code the SQL language with
> synthetic events and histograms?
>
> The language can alredy offer something *way more generic*, out of the
> box, while still covering the desired special cases.
>
> We can support the standard SQL aggregate functions (e.g., MAX(), MIN(),
> SUM(), COUNT(), DISTINCT(), AVG(), etc.) + some kernel-specific
> functions (e.g., PROCESS_NAME(), PROCESS_PRIO(), USECS(), etc.) + the
> standard SQL keyworkds like ORDER BY, LIMIT, DESC, ASC, etc. This would
> offer some nice friendly competition to BPF tracing, while still being a
> (relatively) simple *query-only* language.
>
> I'm not sure if you would be OK with this, but I thought a proposal
> won't hurt :)
>
> I can also write some patches on top of this series if you are OK with
> the principle in general.
>
I'm not against it, and was thinking of implementing some kind of
"trace-cmd sql" feature. But before we can get there, we need a way to
get that information out from the kernel.
-- Steve
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