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Fri, 12 Jun 2026 09:43:37 +0000 (GMT) Received: from [9.39.29.202] (unknown [9.39.29.202]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 12 Jun 2026 09:43:37 +0000 (GMT) Message-ID: Date: Fri, 12 Jun 2026 15:13:36 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 00/10] sched/fair, KVM: Semantics-aware directed yield for oversubscribed KVM To: Wanpeng Li Cc: K Prateek Nayak , Christian Borntraeger , Steven Rostedt , Vincent Guittot , Juri Lelli , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Wanpeng Li , Richie Buturla , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Paolo Bonzini , Sean Christopherson References: <20260612013355.59231-1-kernellwp@gmail.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260612013355.59231-1-kernellwp@gmail.com> 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-ORIG-GUID: 38aQu0V4A06bmCcDx61RmKTvajf7pr3y X-Authority-Analysis: v=2.4 cv=TdKmcxQh c=1 sm=1 tr=0 ts=6a2bd4d2 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=GvQkQWPkAAAA:8 a=dLX7AjkPyFth-2rxqAkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjEyMDA4NiBTYWx0ZWRfX6dLnxyHAH1+g sjYQQQ8daYCx0G1DIICHpMfI6s5IgalLRwZYLw+cpZj34vQQy/051JE6fW0PK6mxKGpWlh5rPET A+5pkmujPnntKUhqY43ciXVLS402D5MHcjj7zx+q+tRDXBd5ivrEEiAd7Zf1OldUmbjwyz87lB/ dbpdlMU2OG0kOlczWssVB9lZi0ZTwTqTPdfFIWDv9XFt04WNZjaAjNL4Xbv4bnnRkASkRkWsJQi msiMSFzrjG3biFKnvIfC747N0tQ/2aLXBhhWbVxcuogOZk79JcjiA3BmyTYzhTH3/u0yV+uk9JN tg0Qtzyw0ThcKYK4jGkVhbj3tj2DrPWvOMsTnfu1bEZKzBj55CfPrDOPQiLZ1090ETkU5wLrtRg Ce32hAzJLwRtX4k5qrCvl5sB4mawV3TJYio3NwMiwJ+dNPa2pjhcpTJS40Ze/OAYrNungz4y/9e gx26Bv9Xuo+umas+WOw== X-Proofpoint-GUID: Z7qOhL-NPrbkCeJDj-DaeabpLNQledXg X-Proofpoint-Spam-Info: AW1haW4tMjYwNjEyMDA4NiBTYWx0ZWRfX7Po8+yadh8Cn F8hkvY+PRNIJXDuwfR6XKWeeQsMhQPjL+5kk276FtesGWJZ5fl2Rkry8aBD74kILBpJaS9QdJvs v6akaT+jO0SI0XgjCxWvxsTWAro32ww= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-12_01,2026-06-11_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 malwarescore=0 clxscore=1011 impostorscore=0 adultscore=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606040000 definitions=main-2606120086 Hi Wanpeng. On 6/12/26 7:03 AM, Wanpeng Li wrote: > From: Wanpeng Li > > On overcommitted hosts, a spinning vCPU often calls yield_to() to let a > lock holder or IPI receiver run. The hint can be ineffective for two > independent reasons: the scheduler may fail to select the nominated task, > and KVM may nominate a task that is not the one the spinning vCPU is > waiting for. > I was curious to try this as we have been working on paravirt scheduling which aims at reducing the vCPU preemption based on the steal time. https://lore.kernel.org/all/20260514152204.481115-1-sshegde@linux.ibm.com/ I gave the patch series a try. With both real life workload(daytrader) and micro-benchmarks (hackbench) I don't see any benefit. Note that it is running the same workloads in all VM's at the same time. I had thought about this series: - Do you observe steal time when you run your workload? If yes, if you reduce the vCPU, IPI will natually move to reduced set and due to reduction in vCPU preemption yeild also may not be necessary. - is there vCPU pinning? workload is pinned separately to explicit vCPUs. - Is only a few vCPUs doing the locks in the workload you have mentioned in the cover-letter?