From: "Shreyas B. Prabhu" <shreyas@linux.vnet.ibm.com>
To: rjw@rjwysocki.net
Cc: daniel.lezcano@linaro.org, linux-pm@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, anton@samba.org,
mpe@ellerman.id.au,
"Shreyas B. Prabhu" <shreyas@linux.vnet.ibm.com>
Subject: [PATCH] cpuidle/powernv: Fix snooze timeout
Date: Wed, 22 Jun 2016 14:36:43 -0500 [thread overview]
Message-ID: <1466624203-1847-1-git-send-email-shreyas@linux.vnet.ibm.com> (raw)
Snooze is a poll idle state in powernv and pseries platforms. Snooze
has a timeout so that if a cpu stays in snooze for more than target
residency of the next available idle state, then it would exit thereby
giving chance to the cpuidle governor to re-evaluate and
promote the cpu to a deeper idle state. Therefore whenever snooze exits
due to this timeout, its last_residency will be target_residency of next
deeper state.
commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()")
changed the math around last_residency calculation. Specifically, while
converting last_residency value from nanoseconds to microseconds it does
right shift by 10. Due to this, in snooze timeout exit scenarios
last_residency calculated is roughly 2.3% less than target_residency of
next available state. This pattern is picked up get_typical_interval()
in the menu governor and therefore expected_interval in menu_select() is
frequently less than the target_residency of any state but snooze.
Due to this we are entering snooze at a higher rate, thereby affecting
the single thread performance.
Since the math around last_residency is not meant to be precise, fix this
issue setting snooze timeout to 105% of target_residency of next
available idle state.
This also adds comment around why snooze timeout is necessary.
Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
---
drivers/cpuidle/cpuidle-powernv.c | 14 ++++++++++++++
drivers/cpuidle/cpuidle-pseries.c | 13 +++++++++++++
2 files changed, 27 insertions(+)
diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index e12dc30..5835491 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -268,10 +268,24 @@ static int powernv_idle_probe(void)
cpuidle_state_table = powernv_states;
/* Device tree can indicate more idle states */
max_idle_state = powernv_add_idle_states();
+
+ /*
+ * Staying in snooze for a long period can degrade the
+ * perfomance of the sibling cpus. Set timeout for snooze such
+ * that if the cpu stays in snooze longer than target residency
+ * of the next available idle state then exit from snooze. This
+ * gives a chance to the cpuidle governor to re-evaluate and
+ * promote it to deeper idle states.
+ */
if (max_idle_state > 1) {
snooze_timeout_en = true;
snooze_timeout = powernv_states[1].target_residency *
tb_ticks_per_usec;
+ /*
+ * Give a 5% margin since target residency related math
+ * is not precise in cpuidle core.
+ */
+ snooze_timeout += snooze_timeout / 20;
}
} else
return -ENODEV;
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index 07135e0..22de841 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -250,10 +250,23 @@ static int pseries_idle_probe(void)
} else
return -ENODEV;
+ /*
+ * Staying in snooze for a long period can degrade the
+ * perfomance of the sibling cpus. Set timeout for snooze such
+ * that if the cpu stays in snooze longer than target residency
+ * of the next available idle state then exit from snooze. This
+ * gives a chance to the cpuidle governor to re-evaluate and
+ * promote it to deeper idle states.
+ */
if (max_idle_state > 1) {
snooze_timeout_en = true;
snooze_timeout = cpuidle_state_table[1].target_residency *
tb_ticks_per_usec;
+ /*
+ * Give a 5% margin since target residency related math
+ * is not precise in cpuidle core.
+ */
+ snooze_timeout += snooze_timeout / 20;
}
return 0;
}
--
2.1.4
next reply other threads:[~2016-06-22 19:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-22 19:36 Shreyas B. Prabhu [this message]
2016-06-22 22:49 ` [PATCH] cpuidle/powernv: Fix snooze timeout Rafael J. Wysocki
2016-06-22 23:48 ` Balbir Singh
2016-06-23 4:58 ` Shreyas B Prabhu
2016-06-23 9:28 ` Balbir Singh
2016-06-23 9:41 ` Shreyas B Prabhu
2016-06-23 9:55 ` Balbir Singh
2016-06-23 10:01 ` Daniel Lezcano
2016-06-23 13:35 ` Shreyas B Prabhu
2016-06-23 14:36 ` Daniel Lezcano
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=1466624203-1847-1-git-send-email-shreyas@linux.vnet.ibm.com \
--to=shreyas@linux.vnet.ibm.com \
--cc=anton@samba.org \
--cc=daniel.lezcano@linaro.org \
--cc=linux-pm@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=rjw@rjwysocki.net \
/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).