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akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@ACULAB.COM, richard@nod.at, mjguzik@gmail.com, Ankur Arora Subject: [RFC PATCH 49/86] osnoise: handle quiescent states directly Date: Tue, 7 Nov 2023 13:57:35 -0800 Message-Id: <20231107215742.363031-50-ankur.a.arora@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20231107215742.363031-1-ankur.a.arora@oracle.com> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> 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X-MS-Exchange-CrossTenant-AuthSource: CO6PR10MB5409.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Nov 2023 22:00:12.4762 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: SD0lmxQN5N3TJJBD8IxgJ5H5vey+MMYHjlMBrGtc4F9Ij0bnbU0G2tWdku63U07pPxgLd+LX6/9XZKCBZPACAsXRy08LCDks3wn+qzrMI5c= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR10MB6275 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-07_13,2023-11-07_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 phishscore=0 suspectscore=0 malwarescore=0 mlxlogscore=802 bulkscore=0 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311060000 definitions=main-2311070182 X-Proofpoint-ORIG-GUID: JWHRUvapECFaZw5SWt8zlEiJOnvpQH91 X-Proofpoint-GUID: JWHRUvapECFaZw5SWt8zlEiJOnvpQH91 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" To reduce RCU noise for the stopped tick case we introduce explicit quiescent states for PREEMPT_RCU=3Dy, and depend on cond_resched() (and thus rcu_all_qs()) to handle PREEMPT_RCU=3Dn. With cond_resched() going away, introduce explicit quiescent states for all configurations. Suggested-by: Paul E. McKenney Signed-off-by: Ankur Arora --- kernel/trace/trace_osnoise.c | 37 ++++++++++++------------------------ 1 file changed, 12 insertions(+), 25 deletions(-) diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index bd0d01d00fb9..db38934c4242 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1531,34 +1531,21 @@ static int run_osnoise(void) =20 /* * In some cases, notably when running on a nohz_full CPU with - * a stopped tick PREEMPT_RCU has no way to account for QSs. - * This will eventually cause unwarranted noise as PREEMPT_RCU - * will force preemption as the means of ending the current - * grace period. We avoid this problem by calling - * rcu_momentary_dyntick_idle(), which performs a zero duration - * EQS allowing PREEMPT_RCU to end the current grace period. - * This call shouldn't be wrapped inside an RCU critical - * section. - * - * Note that in non PREEMPT_RCU kernels QSs are handled through - * cond_resched() + * a stopped tick RCU has no way to account for QSs. This will + * eventually cause unwarranted noise as RCU forces preemption + * as the means of ending the current grace period. + * We avoid this problem by calling rcu_momentary_dyntick_idle(), + * which performs a zero duration EQS allowing RCU to end the + * current grace period. This call shouldn't be wrapped inside + * an RCU critical section. */ - if (IS_ENABLED(CONFIG_PREEMPT_RCU)) { - if (!disable_irq) - local_irq_disable(); + if (!disable_irq) + local_irq_disable(); =20 - rcu_momentary_dyntick_idle(); + rcu_momentary_dyntick_idle(); =20 - if (!disable_irq) - local_irq_enable(); - } - - /* - * For the non-preemptive kernel config: let threads runs, if - * they so wish, unless set not do to so. - */ - if (!disable_irq && !disable_preemption) - cond_resched(); + if (!disable_irq) + local_irq_enable(); =20 last_sample =3D sample; last_int_count =3D int_count; --=20 2.31.1