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Wed, 13 May 2026 06:16:19 +0000 (GMT) Received: from [9.39.28.2] (unknown [9.39.28.2]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 13 May 2026 06:16:19 +0000 (GMT) Message-ID: <5f8e523f-b144-490a-bdda-b6d9ae8bf067@linux.ibm.com> Date: Wed, 13 May 2026 11:46:18 +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 3/3] sched/fair: Add compile time check in fastpaths for CONFIG_SCHED_SMT=n To: K Prateek Nayak , mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Cc: juri.lelli@redhat.com, vschneid@redhat.com, dietmar.eggemann@arm.com, tj@kernel.org, rostedt@goodmis.org, mgorman@suse.de, bsegall@google.com, arighi@nvidia.com References: <20260512152125.308280-1-sshegde@linux.ibm.com> <20260512152125.308280-4-sshegde@linux.ibm.com> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=KbvidwYD c=1 sm=1 tr=0 ts=6a041739 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=GJQ0MKrqjo1CW2UFYi4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTEzMDA2MCBTYWx0ZWRfXydt9YDLUOysE /uJ1CK2UefcDUIEF1k5YZ6ZNCnYxafhe/rJtPw9E/pi1xk+ca/xZXQ/wofBaPUfCEeTHQQeJiNk yS83qOv9yABHHX32aRpxSUqz/9VFG4PBMgcswWPO8cB75eW3j2PR3JJLQ2rbUklxfMiZNgMUdaI zDQR6MBrxfEOSCTT0EkG5whcthXfQDWLBNZU8dg0hgnF4pySaSOrhE+knmOiazgDjpS/MW59qBD Ni5KIo7a852Tx/xTU1KEJ2dDTvZjIG88Oejh66pQoF9uJhGvPK1qzECMpJhINelt1aMYo+r1QcG BqYREFivNLtibLQ4Tx2aYr/RsOTVtVT4Kvco2Yukh88TSsfen7wa+YqsEiXb9uzEposzYfHbFb/ YJkENnmZU3bdX4+E5Kk0l+8UdW7vz+z7piujuNXjCvKb44jRDYYErNv+u3VjKPRkhrhk+UBp7Sk Y9IlRICILL7t+L7aPKA== X-Proofpoint-GUID: yDBBHyE19CdAtBasn2oGCFMB2wi3kNNS X-Proofpoint-ORIG-GUID: bl_ls8BFGzO3XlXW-wHO4I1Uj0MjGZ7m X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-11_05,2026-05-08_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 bulkscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 phishscore=0 spamscore=0 suspectscore=0 clxscore=1015 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605050000 definitions=main-2605130060 On 5/13/26 11:37 AM, K Prateek Nayak wrote: > Hello Shrikanth, > > Thank you for cleaning these bits up! Couple comments below: > > On 5/12/2026 8:51 PM, Shrikanth Hegde wrote: >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 353e31ecaadc..b6f9592b31fd 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -1586,6 +1586,9 @@ static inline bool is_core_idle(int cpu) >> { >> int sibling; >> >> + if (!IS_ENABLED(CONFIG_SCHED_SMT)) >> + return true; > > I think !sched_smt_active() can also return early here. That said ... > If we do below, the rest users already have the checks. So we should be good. I will add a comment saying this expects to be called under sched_smt_active. >> + >> for_each_cpu(sibling, cpu_smt_mask(cpu)) { >> if (cpu == sibling) >> continue; >> @@ -12003,7 +12006,8 @@ static int should_we_balance(struct lb_env *env) > > ... I think the if() above can simply check for sched_smt_active() > before calling is_core_idle() like: > > if (sched_smt_active() && > !(env->sd->flags & SD_SHARE_CPUCAPACITY) && > !is_core_idle(cpu)) { > ... > } > > That way, we ensure we don't call is_core_idle() and the cpumask_and() > unnecessarily on topologies that don't have SMT domain similar to how > sched_use_asym_prio() guards the call to is_core_idle(). > > Thoughts? Ack. Let me edit the v3. I was about to send. > >> * idle has been found, then its not needed to check other >> * SMT siblings for idleness: >> */ >> - cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu)); >> + if (IS_ENABLED(CONFIG_SCHED_SMT)) >> + cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu)); >> continue; >> } >> >