From patchwork Fri Jun 24 08:23:58 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Shreyas B. 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Violators will be prosecuted; Fri, 24 Jun 2016 02:24:05 -0600 X-IBM-Helo: d03dlp01.boulder.ibm.com X-IBM-MailFrom: shreyas@linux.vnet.ibm.com Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id ADDBB1FF0043; Fri, 24 Jun 2016 02:23:48 -0600 (MDT) Received: from b03ledav002.gho.boulder.ibm.com (b03ledav002.gho.boulder.ibm.com [9.17.130.233]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u5O8O4dS49741850; Fri, 24 Jun 2016 01:24:04 -0700 Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D132D13603A; Fri, 24 Jun 2016 02:24:04 -0600 (MDT) Received: from ltchab1.austin.ibm.com (unknown [9.40.193.138]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP id 49765136044; Fri, 24 Jun 2016 02:24:04 -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, bsingharora@gmail.com, "Shreyas B. Prabhu" Subject: [PATCH v2] cpuidle: Fix last_residency division Date: Fri, 24 Jun 2016 03:23:58 -0500 X-Mailer: git-send-email 2.1.4 X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16062408-0016-0000-0000-00000408071C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16062408-0017-0000-0000-000030812EBF Message-Id: <1466756638-2362-1-git-send-email-shreyas@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2016-06-24_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-1606240095 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 replacing right shift by 10 with /1000 while calculating last_residency. Reported-by: Anton Blanchard Bisected-by: Shilpasri G Bhat Signed-off-by: Shreyas B. Prabhu --- Changes in v2 ============= - Fixing it in the cpuidle core code instead of driver code. drivers/cpuidle/cpuidle.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a4d0059..30d67a8 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -218,10 +218,10 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, local_irq_enable(); /* - * local_clock() returns the time in nanosecond, let's shift - * by 10 (divide by 1024) to have microsecond based time. + * local_clock() returns the time in nanosecond, let's + * divide by 1000 to have microsecond based time. */ - diff = (time_end - time_start) >> 10; + diff = (time_end - time_start) / 1000; if (diff > INT_MAX) diff = INT_MAX;