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Thu, 13 Mar 2025 08:30:39 GMT Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 92ECF5805E; Thu, 13 Mar 2025 08:30:40 +0000 (GMT) Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id F1F1358043; Thu, 13 Mar 2025 08:30:35 +0000 (GMT) Received: from [9.204.206.228] (unknown [9.204.206.228]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 13 Mar 2025 08:30:35 +0000 (GMT) Message-ID: <3e31e4b7-d4de-4e23-a208-50effb4894a5@linux.ibm.com> Date: Thu, 13 Mar 2025 14:00:34 +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 From: Madadi Vineeth Reddy Subject: Re: [PATCH v2 3/3] sched/fair: Update comments regarding last and skip buddy To: Adam Li Cc: peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, patches@amperecomputing.com, cl@linux.com, christian.loehle@arm.com, Madadi Vineeth Reddy References: <20241127055610.7076-1-adamli@os.amperecomputing.com> <20241127055610.7076-4-adamli@os.amperecomputing.com> Content-Language: en-US In-Reply-To: <20241127055610.7076-4-adamli@os.amperecomputing.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 2pSgbXXuHDKbgk0yVl5s-yGEY_U90MEC X-Proofpoint-ORIG-GUID: 240dtEDCWCvb_LamnoVI6VcerzrLHjB3 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1093,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-13_04,2025-03-11_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 adultscore=0 clxscore=1011 suspectscore=0 phishscore=0 mlxscore=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2503130066 Hi Adam, On 27/11/24 11:26, Adam Li wrote: > Commit 5e963f2bd465 ("sched/fair: Commit to EEVDF") removed the "last" > and "skip" buddy. Update comments in pick_next_entity(). > > Signed-off-by: Adam Li > Reviewed-by: Madadi Vineeth Reddy > --- > kernel/sched/fair.c | 8 +------- > 1 file changed, 1 insertion(+), 7 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index d5a3b5589e4e..259c56dcdff6 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5602,17 +5602,11 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se) > > static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags); > > -/* > - * Pick the next process, keeping these things in mind, in this order: > - * 1) keep things fair between processes/task groups > - * 2) pick the "next" process, since someone really wants that to run > - * 3) pick the "last" process, for cache locality > - * 4) do not run the "skip" process, if something else is available > - */ > static struct sched_entity * > pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq) > { > /* > + * Pick the "next" buddy, since someone really wants that to run. > * Enabling NEXT_BUDDY will affect latency but not fairness. > */ > if (sched_feat(NEXT_BUDDY) && There is one more reference to LAST_BUDDY in check_preempt_wakeup_fair. Regarding pick_next_entity, the first two points are still valid, so only points 3 and 4 could be removed? Something like below diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9dafb374d76d..379dbcbb24e9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5578,8 +5578,6 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags); * Pick the next process, keeping these things in mind, in this order: * 1) keep things fair between processes/task groups * 2) pick the "next" process, since someone really wants that to run - * 3) pick the "last" process, for cache locality - * 4) do not run the "skip" process, if something else is available */ static struct sched_entity * pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq) @@ -8780,9 +8778,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int * * Note: this also catches the edge-case of curr being in a throttled * group (e.g. via set_curr_task), since update_curr() (in the - * enqueue of curr) will have resulted in resched being set. This - * prevents us from potentially nominating it as a false LAST_BUDDY - * below. + * enqueue of curr) will have resulted in resched being set. */ if (test_tsk_need_resched(rq->curr)) return; Thanks, Madadi Vineeth Reddy