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Tue, 7 Jul 2026 06:55:46 +0000 (GMT) Message-ID: <2efb17e0-3b1f-4275-b5a4-58849ee56034@linux.ibm.com> Date: Tue, 7 Jul 2026 12:25:45 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 19/23] virt/steal_monitor: Provide default method to get num of CPUs for steal ratio To: Yury Norov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org References: <20260701141654.500125-1-sshegde@linux.ibm.com> <20260701141654.500125-20-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: 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-Authority-Analysis: v=2.4 cv=KsJ9H2WN c=1 sm=1 tr=0 ts=6a4ca303 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=YVLwSRtI9ssZgaGdXnAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA3MDA2NCBTYWx0ZWRfX5cMZvEUHENCM qUg3kcPWX5++wG7lmaLHb2eWyiWeeJwHenEiKx05gDGkOSFZPdpy0PeLFT3G2S+ar4VV2ms/Nxb oXQDioa+dMuP9JMSnd/p9Oga4VivljI= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA3MDA2NCBTYWx0ZWRfXw+uG+7wtkHi/ OBpncpmbgTlkV9FaBaGHOuNcVU5RhzYYo3LzEVJAeSp+VyBTrNgn3Uz91riLgtZl+VRglgc11NT pZPsUuNcGznL0ZwQDis9xmAssBkCZdbKQzBQCOHJSIVnuGG3iZCp7FOU/sp8TsgYIGr8+hqUx0i 2EOFJAqhZIOi88dmgOoaIwEm7vR52Kjv+9LSJaYuVZ0Ns6++CBVn6hu2V/QG28/uamQQlD1lX+f YI/ZlD/so2Q5eqLK7StImWmtA5rkuq6+Mo2O8pkpP0ddrApQdUSt3zkA4aIgLLsRpDgIo1z2HL1 B39hGhppYVrxblxZ7InCa/a+B2BesMdUqCqXCpu6QegZVgHWuh1m/m2fKC68kcSyEQk1YiGc6LU +jRBalPd/kuSAdpvIAmhUdiKunmx95JYaQmjBk4Y48rCw8oVMD6pRv4CkomhoRQAAaaT1i1qsov pY8W/59/pHKZMtj+fyA== X-Proofpoint-ORIG-GUID: VFY5i8XSNdNAhLbIBWdYHDs1a1bJnWz- X-Proofpoint-GUID: Tt1IiWpMdcB_89ITNmuotV-lRRtBbShK X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-07_01,2026-07-06_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607070064 On 7/7/26 12:56 AM, Yury Norov wrote: > On Wed, Jul 01, 2026 at 07:46:50PM +0530, Shrikanth Hegde wrote: >> This method informs the steal_monitor core, how many CPUs it needs to >> consider for steal ratio calculations. >> steal_ratio = (delta_steal * 100 * 100) / (delta_ns * number_of_cpus); >> >> Default method returns number of Active CPUs since it calculates steal >> time across active CPUs. >> >> Signed-off-by: Shrikanth Hegde >> --- >> v5->v6: >> - Add cpus_read_lock() for hotplug safety. >> >> drivers/virt/steal_monitor/defaults.c | 11 +++++++++++ >> drivers/virt/steal_monitor/sm_core.h | 1 + >> 2 files changed, 12 insertions(+) >> >> diff --git a/drivers/virt/steal_monitor/defaults.c b/drivers/virt/steal_monitor/defaults.c >> index 4e2e5b233948..70dcfb1ce4cb 100644 >> --- a/drivers/virt/steal_monitor/defaults.c >> +++ b/drivers/virt/steal_monitor/defaults.c >> @@ -27,6 +27,17 @@ u64 __weak get_system_steal_time(void) >> return total_steal; >> } >> >> +/* >> + * Return number of CPUs to consider for steal ratio calculation >> + * >> + * Default returns number of active CPUs. >> + */ >> +unsigned int __weak get_num_cpus_steal_ratio(void) >> +{ >> + guard(cpus_read_lock)(); >> + return num_active_cpus(); >> +} > > How is this lock supposed to work? When you exit the scope, you can be > interrupted and your caller will get outdated information. > > The other callers of num_active_cpus() don't bother taking the lock. > I am thinking i will switch to possible CPUs for steal ratio calculations. That way cumulative steal_values are monotonically increasing and safe against hotplug. That leaves the necessary for locks too. For the SUT it is okay since possible==active. In any systems where it is not, they have edit their default values a bit. Nothing else changes. >> + >> /* >> * Default implementation of decrementing the preferred CPUs based on steal >> * time. This is simple logic and decrease the preferred CPUs by 1 core. >> diff --git a/drivers/virt/steal_monitor/sm_core.h b/drivers/virt/steal_monitor/sm_core.h >> index 030f6236c38e..794d3be04248 100644 >> --- a/drivers/virt/steal_monitor/sm_core.h >> +++ b/drivers/virt/steal_monitor/sm_core.h >> @@ -26,6 +26,7 @@ struct steal_monitor { >> extern struct steal_monitor sm_core_ctx; >> >> u64 get_system_steal_time(void); >> +unsigned int get_num_cpus_steal_ratio(void); >> void increase_preferred_cpus(struct steal_monitor *ctx); >> void decrease_preferred_cpus(struct steal_monitor *ctx); >> >> -- >> 2.47.3