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Violators will be prosecuted; Wed, 22 Jun 2016 13:36:55 -0600 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: shreyas@linux.vnet.ibm.com Received: from b03cxnp07028.gho.boulder.ibm.com (b03cxnp07028.gho.boulder.ibm.com [9.17.130.15]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id E511B19D804E; Wed, 22 Jun 2016 13:36:33 -0600 (MDT) Received: from b03ledav002.gho.boulder.ibm.com (b03ledav002.gho.boulder.ibm.com [9.17.130.233]) by b03cxnp07028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u5MJajWK47382714; Wed, 22 Jun 2016 12:36:55 -0700 Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D751136043; Wed, 22 Jun 2016 13:36:55 -0600 (MDT) Received: from ltchab1.austin.ibm.com (unknown [9.40.193.138]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP id B9DCC136060; Wed, 22 Jun 2016 13:36:54 -0600 (MDT) From: "Shreyas B. Prabhu" 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" Subject: [PATCH] cpuidle/powernv: Fix snooze timeout Date: Wed, 22 Jun 2016 14:36:43 -0500 X-Mailer: git-send-email 2.1.4 X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16062219-0012-0000-0000-00000FFFF401 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16062219-0013-0000-0000-000042FCCE96 Message-Id: <1466624203-1847-1-git-send-email-shreyas@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2016-06-22_11:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606220198 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 Signed-off-by: Shreyas B. Prabhu --- 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; }