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mu4e 1.4.10; emacs 27.2 From: Ankur Arora To: Peter Zijlstra Cc: Ankur Arora , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, 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, rostedt@goodmis.org, tglx@linutronix.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED In-reply-to: <20230909091104.GA2771@noisy.programming.kicks-ass.net> Date: Sat, 09 Sep 2023 13:04:49 -0700 Message-ID: <878r9f5d0e.fsf@oracle.com> Content-Type: text/plain X-ClientProxiedBy: MW4PR04CA0284.namprd04.prod.outlook.com (2603:10b6:303:89::19) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: 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x/K6TBSyp3z7+kvCj6BRfrGPhwV1Czkr8z/3sm4WW985cLJpvn3rKzsTRBn+ZQdx+WM4JBO3k65beQvc4dvh3Gl77uIL1VpgH7R2aFDD4+4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR10MB4297 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-09_19,2023-09-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 adultscore=0 phishscore=0 spamscore=0 mlxlogscore=463 bulkscore=0 suspectscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309090185 X-Proofpoint-ORIG-GUID: qcjMijoCgzKMR7i-GPJ4akb3btCktSwO X-Proofpoint-GUID: qcjMijoCgzKMR7i-GPJ4akb3btCktSwO Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra writes: > On Fri, Sep 08, 2023 at 11:39:47PM -0700, Ankur Arora wrote: > >> Yeah, exactly. Though, not even a single context level, but a flag >> attached to a single context at the process level only. Using >> preempt_count() == 0 as the preemption boundary. >> >> However, this has a problem with the PREEMPT_COUNT=n case because that >> doesn't have a preemption boundary. > > So, with a little sleep, the nested exception/interrupt case should be > good, irqenrty_enter() / irqentry_nmi_enter() unconditionally increment > preempt_count with HARDIRQ_OFFSET / NMI_OFFSET. > > So while regular preempt_{dis,en}able() will turn into a NOP, the entry > code *will* continue to increment preempt_count. Right, I was talking about the regular preempt_disable()/_enable() that will turn into a NOP with PREEMPT_COUNT=n. Actually, let me reply to the mail where you had described this case. -- ankur