From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rZZby5HW6zDqRd for ; Thu, 23 Jun 2016 05:37:02 +1000 (AEST) Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u5MJY6n1078717 for ; Wed, 22 Jun 2016 15:37:00 -0400 Received: from e35.co.us.ibm.com (e35.co.us.ibm.com [32.97.110.153]) by mx0b-001b2d01.pphosted.com with ESMTP id 23q6r4vs7c-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 22 Jun 2016 15:37:00 -0400 Received: from localhost by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 22 Jun 2016 13:36:59 -0600 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 Message-Id: <1466624203-1847-1-git-send-email-shreyas@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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; } -- 2.1.4