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Fri, 27 Feb 2026 15:28:33 +0000 (GMT) Message-ID: Date: Fri, 27 Feb 2026 20:58:33 +0530 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched: Further restrict the preemption modes To: Steven Rostedt Cc: Peter Zijlstra , juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, clrkwllms@kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Linus Torvalds , mingo@kernel.org, Thomas Gleixner , Sebastian Andrzej Siewior , Madhavan Srinivasan , Nicholas Piggin , sathvika@linux.ibm.com References: <20251219101502.GB1132199@noisy.programming.kicks-ass.net> <20260225105345.GZ1282955@noisy.programming.kicks-ass.net> <20260225194809.1f5e44a6@fedora> <127c4772-7352-41a8-b30d-8b869751e907@linux.ibm.com> <20260226122252.184254cd@gandalf.local.home> <97dd1a4f-e524-4337-bcbb-9cbe4bfdda30@linux.ibm.com> <20260227095334.40768d0b@gandalf.local.home> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20260227095334.40768d0b@gandalf.local.home> 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-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjI3MDEzNSBTYWx0ZWRfX+XjernRZcurH 0AjZqAHRU29WTafDUQxfU4JT3gOR9+3/hEds+6cLqcno/b/69h3lVEluPX0c0Nw5CS6xKz/UEUZ El7VW9r53MQRS3xKAba9JmcycD6tkHoh09ETrBGuOsl03wSQnkeOYiP9XZShv+bTvd/vWwK+bxU eJz33TEDE5NukTWp7GGaRZ6Z8/CD6FSA+PqAi9CG2qaZX8YsQMrHxez2uB1Sr8KhT9aVECPAuDK v24gE1/GBa5/j3yxAafQZmxsrX1e3LA4WxQGAqFgjFdnxP+7P5nK+96yGKKX3YIL9ccnvsof/OO 3D3eAp/EoBLuEaDp4HBVz+oqgcyVt6aaRHi6Um7v+ZcWX2GbqUEN6npwnR0JKgr22QtErKkRu/e BJYqWpw6IPJlmr4i7e6FNzBDHKdnnC0IgHjjjiDP8qcXdhJOXo2zNrunko3LTUQxmqtA+HonaV6 58tWN1XuCa+nbx/ISQA== X-Proofpoint-GUID: 8zQxxccwEctrSl2Q9p-a42gYVbz4yGAg X-Authority-Analysis: v=2.4 cv=S4HUAYsP c=1 sm=1 tr=0 ts=69a1b82b cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VnNF1IyMAAAA:8 a=oz0MBj8qPJYlR2GuimMA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: -L8JRbTqcWANa-ACoocBd0aEz-Pd2lV9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-27_02,2026-02-27_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 clxscore=1015 impostorscore=0 malwarescore=0 bulkscore=0 phishscore=0 adultscore=0 lowpriorityscore=0 spamscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602270135 Hi Steve. On 2/27/26 8:23 PM, Steven Rostedt wrote: > On Fri, 27 Feb 2026 14:39:42 +0530 > Shrikanth Hegde wrote: > >> I am afraid we will have trace all functions to begin with (which is expensive), but filter >> out those which took minimal time (like less than a 1s or so). that would eventually leave only a >> few functions that actually took more than 1s(that should have limited overhead). > > Well, I think the detection can be done with timings between schedules. > What's the longest running task without any voluntary schedule. Then you > can add function graph tracing to it where it can possibly trigger in the > location that detected the issue. > > On a detection of a long schedule, a stack trace can be recorded. Using > that stack trace, you could use the function graph tracer to see what is > happening. > > Anyway, something to think about, and this could be a topic at this years > Linux Plumbers Tracing MC ;-) > Yep. Will try to do this. Someone from our tracing team wanted to give this a try too. Lets see. > -- Steve