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Violators will be prosecuted; Fri, 1 Jul 2016 10:24:25 -0400 X-IBM-Helo: d01dlp02.pok.ibm.com X-IBM-MailFrom: shreyas@linux.vnet.ibm.com Received: from b01cxnp22033.gho.pok.ibm.com (b01cxnp22033.gho.pok.ibm.com [9.57.198.23]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id C92746E803F; Fri, 1 Jul 2016 10:24:05 -0400 (EDT) Received: from b01ledav002.gho.pok.ibm.com (b01ledav002.gho.pok.ibm.com [9.57.199.107]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u61EOOHT49283162; Fri, 1 Jul 2016 14:24:24 GMT Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 07B3212403F; Fri, 1 Jul 2016 10:24:24 -0400 (EDT) Received: from ltchab1.austin.ibm.com (unknown [9.40.193.138]) by b01ledav002.gho.pok.ibm.com (Postfix) with ESMTP id 70B4F12403D; Fri, 1 Jul 2016 10:24:23 -0400 (EDT) From: "Shreyas B. Prabhu" To: rjw@rjwysocki.net Cc: linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, daniel.lezcano@linaro.org, nicolas.pitre@linaro.org, bsingharora@gmail.com, "Shreyas B. Prabhu" Subject: [PATCH v5] cpuidle: Fix last_residency division Date: Fri, 1 Jul 2016 09:24:14 -0500 X-Mailer: git-send-email 2.1.4 X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16070114-0056-0000-0000-000000AD3A3C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16070114-0057-0000-0000-000004C732CB Message-Id: <1467383054-1959-1-git-send-email-shreyas@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2016-07-01_04:, , 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-1607010144 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. Fix this by using precise division via ktime_us_delta. Reported-by: Anton Blanchard Bisected-by: Shilpasri G Bhat Signed-off-by: Shreyas B. Prabhu Acked-by: Daniel Lezcano Acked-by: Balbir Singh --- Changes in v5 ============= - Replacing approximation division with ktime_us_delta. Changes in v4 ============= - Increasing the threshold upto which approximation can be used. - Removed explicit cast. Instead added a comment saying why cast is safe. Changes in v3 ============= - Using approximation suggested by David Changes in v2 ============= - Fixing it in the cpuidle core code instead of driver code. drivers/cpuidle/cpuidle.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a4d0059..c73207a 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -173,7 +173,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, struct cpuidle_state *target_state = &drv->states[index]; bool broadcast = !!(target_state->flags & CPUIDLE_FLAG_TIMER_STOP); - u64 time_start, time_end; + ktime_t time_start, time_end; s64 diff; /* @@ -195,13 +195,13 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, sched_idle_set_state(target_state); trace_cpu_idle_rcuidle(index, dev->cpu); - time_start = local_clock(); + time_start = ns_to_ktime(local_clock()); stop_critical_timings(); entered_state = target_state->enter(dev, drv, index); start_critical_timings(); - time_end = local_clock(); + time_end = ns_to_ktime(local_clock()); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); /* The cpu is no longer idle or about to enter idle. */ @@ -217,11 +217,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, if (!cpuidle_state_is_coupled(drv, index)) local_irq_enable(); - /* - * local_clock() returns the time in nanosecond, let's shift - * by 10 (divide by 1024) to have microsecond based time. - */ - diff = (time_end - time_start) >> 10; + diff = ktime_us_delta(time_end, time_start); if (diff > INT_MAX) diff = INT_MAX;