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Wed, 19 Nov 2025 12:53:33 +0000 (GMT) Message-ID: Date: Wed, 19 Nov 2025 18:23:33 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 00/17] Paravirt CPUs and push task for less vCPU preemption To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, gregkh@linuxfoundation.org, christophe.leroy@csgroup.eu Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, yury.norov@gmail.com, maddy@linux.ibm.com, srikar@linux.ibm.com, pbonzini@redhat.com, seanjc@google.com, kprateek.nayak@amd.com, vschneid@redhat.com, iii@linux.ibm.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com References: <20251119062100.1112520-1-sshegde@linux.ibm.com> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20251119062100.1112520-1-sshegde@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: jNM7PZpv00Dfc7PPG9KvyQC4p4AvRGBC X-Proofpoint-ORIG-GUID: wh1nhdpadEQFd8dGH0QXNTHWScvNvbyu X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfX2iW4gQ4pUNtW n6B/i2d6o/W8wT11Dw7L4mgpNuZrDJfMajENMMRVWHZIsqwoRNyHF2/6BWuILghUB7cChkKgD7s y2JIdi6JoOIz1dMOkqTu/dCnHsSIirmMjRASApGJMSgxiilskmh7UR406g9GTdAz2j4bIry9R0Z 4iATnUCFf3WCxeEiq/u24+VqmURMHAfHftzdYPByR4EMRJTyUig5hL0hC4q7Mg76GKvZsjUyl0t LA7YvzDB7i/NRXxv4C+bRy9sBM9E4G3coMU0jjYaNzV+HVXIyJQ7HPnvwlKO/2PGvqP+gXrxVCq OyzcT300iRlEVDV2v7bz0yrW9wGfHPEdojOtGuzAaegG/+qJB1/JmBOSnu1mkjoRg2J3Mlo57bJ XS3gIOTDEuYHTdvt9DLVPq11i/8TTQ== X-Authority-Analysis: v=2.4 cv=SvOdKfO0 c=1 sm=1 tr=0 ts=691dbdd6 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=Pi4crXe-Rn3qxXpBZEsA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-19_03,2025-11-18_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 clxscore=1015 suspectscore=0 phishscore=0 adultscore=0 bulkscore=0 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 On 11/19/25 11:50 AM, Shrikanth Hegde wrote: > Detailed problem statement and some of the implementation choices were > discussed earlier[1]. > > [1]: https://lore.kernel.org/all/20250910174210.1969750-1-sshegde@linux.ibm.com/ > > This is likely the version which would be used for LPC2025 discussion on > this topic. Feel free to provide your suggestion and hoping for a solution > that works for different architectures and it's use cases. > > All the existing alternatives such as cpu hotplug, creating isolated > partitions etc break the user affinity. Since number of CPUs to use change > depending on the steal time, it is not driven by User. Hence it would be > wrong to break the affinity. This series allows if the task is pinned > only paravirt CPUs, it will continue running there. > > Changes compared v3[1]: > > - Introduced computation of steal time in powerpc code. > - Derive number of CPUs to use and mark the remaining as paravirt based > on steal values. > - Provide debugfs knobs to alter how steal time values being used. > - Removed static key check for paravirt CPUs (Yury) > - Removed preempt_disable/enable while calling stopper (Prateek) > - Made select_idle_sibling and friends aware of paravirt CPUs. > - Removed 3 unused schedstat fields and introduced 2 related to paravirt > handling. > - Handled nohz_full case by enabling tick on it when there is CFS/RT on > it. > - Updated helper patch to override arch behaviour for easier debugging > during development. Sorry for creating confusion around last two patches. Sent out new version. https://lore.kernel.org/all/20251119124449.1149616-1-sshegde@linux.ibm.com/