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Thu, 11 Sep 2025 15:56:58 +0000 (GMT) Message-ID: Date: Thu, 11 Sep 2025 21:26:56 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v3 05/10] sched/fair: Don't consider paravirt CPUs for wakeup and load balance To: K Prateek Nayak Cc: vschneid@redhat.com, iii@linux.ibm.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, vineeth@bitbyteword.org, jgross@suse.com, pbonzini@redhat.com, seanjc@google.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, yury.norov@gmail.com, maddy@linux.ibm.com, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, gregkh@linuxfoundation.org References: <20250910174210.1969750-1-sshegde@linux.ibm.com> <20250910174210.1969750-6-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: EoQsnxEWE1fI354CANC2daJRZduOKjwS X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA2MDIzNSBTYWx0ZWRfX40KWbzuYW4yb HAkT/MkP3dT8oVyRGsBmRbDj8DxlBiVmoppZy4vOpQlrlkaNFcagd7duMX8LekGfxPqeiWxbPCG 0jdB9Uq2b28bszHS69d9zU/QCuccRH25xJW8jgMJFfQUUnr9eA5TJVGmR6B+V3cZ3ubgN5ztd4A DkCgZoDxs0+/luDXoaIXiBJGs2VAxUneyqzv0jRWEBsYMZAyuofYeEukbYDT0/r42fqNiLgt8Jr 2n1GIHqgt3XMBKNrPB01/0UoAgMYt+YiAveDpD018CWULDfRrayT1JPThOu4R1VAt7eDdUQRxfD XhYXBPPE5H16s5a9vZQQx/oFEav6qSbZXNZ9cOM3BhC2McMszLw5IX5stZzgm/WAhZR9If2yIpC SGIfN9Dr X-Proofpoint-GUID: snWUdQdLKZTGcpGH5mLV10L87_zdZ_yv X-Authority-Analysis: v=2.4 cv=F59XdrhN c=1 sm=1 tr=0 ts=68c2f158 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=ex1m0Fpx1afbAyXWguEA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-09-11_02,2025-09-11_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 clxscore=1015 impostorscore=0 bulkscore=0 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2509060235 On 9/11/25 10:53 AM, K Prateek Nayak wrote: > Hello Shrikanth, > > On 9/10/2025 11:12 PM, Shrikanth Hegde wrote: >> @@ -8563,7 +8563,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) >> if (!is_rd_overutilized(this_rq()->rd)) { >> new_cpu = find_energy_efficient_cpu(p, prev_cpu); >> if (new_cpu >= 0) >> - return new_cpu; >> + goto check_new_cpu; > > Should this fallback to the overutilized path if the most energy > efficient CPU is found to be paravirtualized or should > find_energy_efficient_cpu() be made aware of it? > >> new_cpu = prev_cpu; >> } >> >> @@ -8605,7 +8605,12 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) >> } >> rcu_read_unlock(); >> >> - return new_cpu; >> + /* If newly found or prev_cpu is a paravirt cpu, use current cpu */ >> +check_new_cpu: >> + if (is_cpu_paravirt(new_cpu)) >> + return cpu; >> + else > > nit. redundant else. > Do you mean "is_cpu_paravirt(new_cpu) ? cpu; new_cpu" This needs to return cpu instead of true/false. maybe i not seeing the obvious. >> + return new_cpu; >> } >> >> /* >> @@ -11734,6 +11739,12 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq, >> >> cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask); >> >> +#ifdef CONFIG_PARAVIRT >> + /* Don't spread load to paravirt CPUs */ >> + if (static_branch_unlikely(&cpu_paravirt_push_tasks)) >> + cpumask_andnot(cpus, cpus, cpu_paravirt_mask); >> +#endif > > Can something similar be also be done in select_idle_sibling() and > sched_balance_find_dst_cpu() for wakeup path? That's a good suggestion. don't make a choice which is a paravirt CPU. Will explore. > >> + >> schedstat_inc(sd->lb_count[idle]); >> >> redo: