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Thu, 29 Feb 2024 04:46:55 GMT Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 702CE58061; Thu, 29 Feb 2024 04:46:53 +0000 (GMT) Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B33E55805C; Thu, 29 Feb 2024 04:46:48 +0000 (GMT) Received: from [9.109.201.126] (unknown [9.109.201.126]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 29 Feb 2024 04:46:48 +0000 (GMT) Message-ID: Date: Thu, 29 Feb 2024 10:16:47 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/2] sched/fair: Limit access to overutilized Content-Language: en-US To: Qais Yousef Cc: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, yu.c.chen@intel.com, dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org, nysal@linux.ibm.com, aboorvad@linux.ibm.com, srikar@linux.vnet.ibm.com, vschneid@redhat.com, pierre.gondois@arm.com, morten.rasmussen@arm.com References: <20240228071621.602596-1-sshegde@linux.ibm.com> <20240229000817.n2bnr4kioigaqtct@airbuntu> From: Shrikanth Hegde In-Reply-To: <20240229000817.n2bnr4kioigaqtct@airbuntu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: gdikrROokuNS7VWchLzpdurmXl9rRuZf X-Proofpoint-ORIG-GUID: bT1nYwcRrlPwGD45CyWhVpK2OEOrlEnE X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-28_08,2024-02-27_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 spamscore=0 mlxlogscore=999 impostorscore=0 malwarescore=0 adultscore=0 clxscore=1015 mlxscore=0 bulkscore=0 suspectscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2402290035 On 2/29/24 5:38 AM, Qais Yousef wrote: > On 02/28/24 12:46, Shrikanth Hegde wrote: [...] >> Overutilized was added for EAS(Energy aware scheduler) to choose either >> EAS aware load balancing or regular load balance. As checked, on x86 and > > It actually toggles load balance on/off (off if !overutilized). > > misfit load balance used to be controlled by this but this was decoupled since > commit e5ed0550c04c ("sched/fair: unlink misfit task from cpu overutilized") > Ok. >> powerpc both overload and overutilized share the same cacheline in rd. >> Updating overutilized is not required for non-EAS platforms. > > Is the fact these two share the cacheline is part of the problem? From patch > 1 it seems the fact that overutlized is updated often on different cpus is the > problem? Did you try to move overutlized to different places to see if this > alternatively helps? > > The patches look fine to me. I am just trying to verify that indeed the access > to overutilzed is the problem, not something else being on the same cacheline > is accidentally being slowed down, which means the problem can resurface in the > future. > We did explicit cachealign for overload. By doing that newidle_balance goes away from perf profile. But enqueue_task_fair still remains. That because there is load-store tearing happening on overutilized field alone due to different CPUs accessing and updating it at the same time. We have also verified that rq->rd->overutilized in enqueue_task_fair path is the reason for it showing up in perf profile. >> [...] >> >> -- >> 2.39.3 >>