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Tue, 7 Oct 2025 05:12:35 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5946320040; Tue, 7 Oct 2025 05:12:35 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D04A220043; Tue, 7 Oct 2025 05:12:30 +0000 (GMT) Received: from [9.39.21.122] (unknown [9.39.21.122]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 7 Oct 2025 05:12:30 +0000 (GMT) Message-ID: <2b37d74f-7a5d-486b-98df-679bd7e2b0c2@linux.ibm.com> Date: Tue, 7 Oct 2025 10:42:29 +0530 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/14] sched: Employ sched_change guards To: Peter Zijlstra Cc: linux-kernel@vger.kernel.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, longman@redhat.com, hannes@cmpxchg.org, mkoutny@suse.com, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, cgroups@vger.kernel.org, sched-ext@lists.linux.dev, liuwenfang@honor.com, tglx@linutronix.de, tj@kernel.org References: <20250910154409.446470175@infradead.org> <20250910155808.415580225@infradead.org> <20251006181429.GV3245006@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20251006181429.GV3245006@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=EqnfbCcA c=1 sm=1 tr=0 ts=68e4a147 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=qX6ajofIpXMs4fIIw1kA:9 a=QEXdDO2ut3YA:10 a=nl4s5V0KI7Kw-pW0DWrs:22 a=pHzHmUro8NiASowvMSCR:22 a=xoEH_sTeL_Rfw54TyV31:22 X-Proofpoint-GUID: cAqOOaCKutzRGHdSxvZApmpDB_dpjxLd X-Proofpoint-ORIG-GUID: euvDvoERsB13dXaex28twqgFbv7-s7Ba X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDAzMDIwMSBTYWx0ZWRfX32bytjmGzGCV UjpUqZMEWxRLOY1FL939p/tPFpycFWvvjDJDzsR4KycttyTHbQYa4OoMvsQMOs7zBuM9nitRwQs PT1t1OhhYoQzFgug9w9SWc6CaoCha8EBxdz0Cqf7tcSENBQJcR1kw/JujHtem1EkfKL/3XRQPCg kBRssF+nr52FI08nuAvCvqSfhz8UUwR9syE+4nUKmFGsGk9c0dBfSGDNbJUO7sEViryWf7bfeLL MsFssEmH07hcWNnkQivz/5j0xbRYossatwPrinkaHCl1y3dUyjv/C0SjnDq2QFYtIyF+W45GNvi BvcTr1RbeeNyI4UCFmkN2oerfX1fJ2ZwRIoqTGYm/JUq6ztlDUF9Y1AnKdPENmlZPK4U8Lh/x1o eE1uAA0HsB132IpaqyedhF9lRk5TMQ== 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=2025-10-06_07,2025-10-06_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 impostorscore=0 adultscore=0 phishscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2509150000 definitions=main-2510030201 On 10/6/25 11:44 PM, Peter Zijlstra wrote: > On Mon, Oct 06, 2025 at 08:51:27PM +0530, Shrikanth Hegde wrote: >> >> >> On 9/10/25 9:14 PM, Peter Zijlstra wrote: >>> As proposed a long while ago -- and half done by scx -- wrap the >>> scheduler's 'change' pattern in a guard helper. >>> >> [...]> put_task_struct(p); >>> --- a/kernel/sched/sched.h >>> +++ b/kernel/sched/sched.h >>> @@ -3860,23 +3860,22 @@ extern void check_class_changed(struct r >>> extern struct balance_callback *splice_balance_callbacks(struct rq *rq); >>> extern void balance_callbacks(struct rq *rq, struct balance_callback *head); >>> -#ifdef CONFIG_SCHED_CLASS_EXT >>> -/* >>> - * Used by SCX in the enable/disable paths to move tasks between sched_classes >>> - * and establish invariants. >>> - */ >>> -struct sched_enq_and_set_ctx { >>> +struct sched_change_ctx { >>> struct task_struct *p; >>> - int queue_flags; >>> + int flags; >>> bool queued; >>> bool running; >>> }; >>> -void sched_deq_and_put_task(struct task_struct *p, int queue_flags, >>> - struct sched_enq_and_set_ctx *ctx); >>> -void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx); >>> +struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags); >>> +void sched_change_end(struct sched_change_ctx *ctx); >>> -#endif /* CONFIG_SCHED_CLASS_EXT */ >>> +DEFINE_CLASS(sched_change, struct sched_change_ctx *, >>> + sched_change_end(_T), >>> + sched_change_begin(p, flags), >>> + struct task_struct *p, unsigned int flags) >>> + >>> +DEFINE_CLASS_IS_UNCONDITIONAL(sched_change) >>> #include "ext.h" >> could you please add a comment on matching flags on dequeue/enqueue >> here? > > Would something like so be okay? This assumes at least the second patch > is applied as well. > > --- > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -10783,6 +10783,12 @@ struct sched_change_ctx *sched_change_be > struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx); > struct rq *rq = task_rq(p); > > + /* > + * Must exclusively use matched flags since this is both dequeue and > + * enqueue. > + */ yes. Something like that. Unless callsites explicitly change the flags using the scope, enqueue will happen with matching flags. > + WARN_ON_ONCE(flags & 0xFFFF0000); > + A mythical example: scope_guard(sched_change, p, DEQUEUE_THROTTLE) scope->flags &= ~DEQUEUE_THROTTLE; scope->flags |= ENQUEUE_HEAD; But, One could still do this right? for such users the warning may be wrong. > lockdep_assert_rq_held(rq); > > if (!(flags & DEQUEUE_NOCLOCK)) {