From: "Doug Smythies" <dsmythies@telus.net>
To: "'Giovanni Gherdovich'" <ggherdovich@suse.cz>
Cc: "'Linux PM'" <linux-pm@vger.kernel.org>,
"'Srinivas Pandruvada'" <srinivas.pandruvada@linux.intel.com>,
"'Peter Zijlstra'" <peterz@infradead.org>,
"'LKML'" <linux-kernel@vger.kernel.org>,
"'Frederic Weisbecker'" <frederic@kernel.org>,
"'Mel Gorman'" <mgorman@suse.de>,
"'Daniel Lezcano'" <daniel.lezcano@linaro.org>,
"'Rafael J. Wysocki'" <rjw@rjwysocki.net>,
"Doug Smythies" <dsmythies@telus.net>
Subject: RE: [RFC/RFT][PATCH v2] cpuidle: New timer events oriented governor for tickless systems
Date: Mon, 5 Nov 2018 14:09:54 -0800 [thread overview]
Message-ID: <002601d47554$4a150060$de3f0120$@net> (raw)
In-Reply-To: JkGTgcRwED1yAJkGYggSqP
On 2018.11.05 11:14 Giovanni Gherdovich wrote:
> On Sun, 2018-11-04 at 11:06 +0100, Rafael J. Wysocki wrote:
>>
>> You can use the cpu_idle trace point to correlate the selected state index
>> with the observed idle duration (that's what Doug did IIUC).
>
> True, that works; although I ended up slapping a tracepoint right at the
> beginning of the teo_update() and capturing the variables
> cpu_data->last_state, dev->last_residency and dev->cpu.
>
> I should have some plots to share soon. I really wanted to do in-kernel
> histograms with systemtap as opposed to collecting data with ftrace and doing
> post-processing, because I noticed that the latter approach generates lots of
> events and wakeups from idle on the cpu that handles the ftrace data. It's
> kind of a workload in itself and spoils the results.
I agree that we need to be careful not to influence the system we
are trying to acquire diagnostic data on via the act of acquiring
that data.
I did not find much, if any, effect of acquiring trace data during the
dbench with 12 clients test. Regardless I do the exact same test the exact
same way for the baseline reference kernel and the test kernel. To be
clear, I mean no effect while actually acquiring the trace samples.
Obviously there is a significant effect while the samples are eventually
written out to disk, after being acquired. But at that point, I don’t care.
For tests where I am also acquiring long term idle statistics, over many
hours, I never run a trace at the same time, and only sample the system once
per minute. For those test scenarios, when a trace is required, i.e. for
greater detail, it is done as an independent step. But yes, for my very high
idle state 0 entry/exit per unit time type tests, enabling trace has a very
significant effect on the system under test. I haven't figured out a way around that.
For example the test where ~6 gigabytes of trace data was collected in
2 minutes, at a cost of ~25% performance drop
(https://marc.info/?l=linux-pm&m=153897853630373&w=2)
For comparison, the 12 client Phoronix dbench test trace on kernel 4.20-rc1
(baseline reference for TEO V3 tests) was only 199 Megabytes in 10 minutes.
... Doug
next prev parent reply other threads:[~2018-11-05 22:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-26 9:12 [RFC/RFT][PATCH v2] cpuidle: New timer events oriented governor for tickless systems Rafael J. Wysocki
2018-10-31 18:36 ` Giovanni Gherdovich
2018-11-04 10:06 ` Rafael J. Wysocki
2018-11-05 19:14 ` Giovanni Gherdovich
2018-11-05 22:09 ` Doug Smythies [this message]
2018-10-27 6:37 Doug Smythies
2018-10-30 7:19 ` Rafael J. Wysocki
2018-11-02 15:39 Doug Smythies
2018-11-04 10:06 ` Rafael J. Wysocki
2018-11-05 19:11 ` Giovanni Gherdovich
2018-11-05 21:28 ` Doug Smythies
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='002601d47554$4a150060$de3f0120$@net' \
--to=dsmythies@telus.net \
--cc=daniel.lezcano@linaro.org \
--cc=frederic@kernel.org \
--cc=ggherdovich@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=peterz@infradead.org \
--cc=rjw@rjwysocki.net \
--cc=srinivas.pandruvada@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).