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Thu, 3 Sep 2026 06:34:22 +0000 (GMT) From: Shrikanth Hegde To: 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, meted@linux.ibm.com, ynorov@nvidia.com Cc: sshegde@linux.ibm.com, 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, jgross@suse.com, virtualization@lists.linux.dev, sunlightlinux@gmail.com Subject: [PATCH v12 11/13] virt/steal_governor: Add control knobs for handling steal values Date: Thu, 3 Sep 2026 12:02:38 +0530 Message-ID: <20260903063240.268775-12-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260903063240.268775-1-sshegde@linux.ibm.com> References: <20260903063240.268775-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: GqZXYbUpnz70K4pKXm7MMeCtlRoGtXVr X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAzMDA1NyBTYWx0ZWRfX31xiiCG3Ewyw wsK0oExE4IkjGzpRjUytnsabNTuiIsnA/jfUboOW5uVL2xL9yedVJqpnch8KpYLuiGUU94tjJTz Qz32eXL/6N+Ec0wx2I3d0gozgwVjYuwSD6TTA00ule0xdDaRxu52VUfMZQGTxEovseR3ZB5HDD0 s3ZA2EPSGC55MHv4lhvcUlRqWI6TzUuCOnGeqOH1Rl95L244iHXgHFMDW+Bx1UuywFqfyBVaeEB dspw78Agt19XDCq/IqQcjtv54RWjxB7WCbx4CTNXuaG54wPZtjKTA7MeeEzWXGmxIkk4AseeIyk gkL+S8NyC1J5dMl2WNIuB7Pi4Ew7BQCF8+IRXZTtnw97xJVPMGG7kvXSU0MdTON1FKRLmvv5mn+ jTa957Kthp8GRfOZ1N3wc3tb/HDJb0v5XFngx7a6AO6/RV0kv0vQvJjrU3E5uP7BquX27WVtMfE X0p9n+rxYAc8aRFjv3Q== X-Proofpoint-ORIG-GUID: 21iAHDdsa1zKU7H_Tbiw8M8aYE7plB63 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAzMDA1NyBTYWx0ZWRfX4LMEFnIkkLHU uDDK2AGkvcudc/JJmliky4aIfTW2Q3ZsKMs1S9LnpKqIZ+yPOqogyiaBcbiLYVCgVoM1L6hZQ0z ZKMbRqjp6uuP9MHrr6cOfKmsVHMKnWM= X-Authority-Analysis: v=2.4 cv=B92JFutM c=1 sm=1 tr=0 ts=6a9914fc cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=pGLkceISAAAA:8 a=VnNF1IyMAAAA:8 a=XC_GqrfF-lTPz34eE_0A:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-03_02,2026-09-02_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609030057 These are the knobs to control the steal_governor. interval_ms: How often steal governor checks for steal time. (Default: 1000 i.e 1 second) This controls how fast steal governor driver reacts to changes to the contention of physical CPUs. Can be set between 100 to 100000. i.e. 100ms to 100seconds. 100ms is kept as minimum to ensure few meaningful steal values accumulate even with HZ=100. low_threshold: lower threshold value in percentage * 100. (Default: 200, i.e 2% steal is considered as low threshold) This determines what values should be considered as nil/no steal values. When steal governor see steal ratio is below or equal to this value, it will increase the preferred CPUs by 1 core. Having value as zero might cause oscillations high_threshold: higher threshold value in percentage * 100 (Default: 500, i.e 5% steal is considered as high threshold) This determines what values should be considered as high steal values. When steal governor sees steal ratio is higher than this value, it will reduce the preferred CPUs by 1 core. module_param_cb methods are used to do the validation checks. This helps to ensure one configures sane values. Since low and high are dependent, that check is done at module init. Notes: - Parameters values can't be changed at runtime. One has to unload the module and change it. Hence recommended to build it as module. - Default values may not work well for all configurations. Tune it according to the system under test. Documentation is available at: Documentation/driver-api/steal-governor.rst Suggested-by: Yury Norov Signed-off-by: Shrikanth Hegde --- drivers/virt/steal_governor.c | 73 ++++++++++++++++++++++++++++++++++- 1 file changed, 71 insertions(+), 2 deletions(-) diff --git a/drivers/virt/steal_governor.c b/drivers/virt/steal_governor.c index 2320cbfa4b47..27f53ea16498 100644 --- a/drivers/virt/steal_governor.c +++ b/drivers/virt/steal_governor.c @@ -40,7 +40,11 @@ struct steal_governor { struct delayed_work work; }; -static struct steal_governor sg_ctx; +static struct steal_governor sg_ctx = { + .interval_ms = 1000, /* 1 second */ + .high_threshold = 500, /* 5% */ + .low_threshold = 200, /* 2% */ +}; static void restore_preferred_to_active(void) { @@ -51,6 +55,62 @@ static void restore_preferred_to_active(void) set_cpu_preferred(cpu, true); } +static int param_set_interval_ms(const char *val, const struct kernel_param *kp) +{ + unsigned int interval; + int ret; + + ret = kstrtouint(val, 0, &interval); + if (ret) + return ret; + + if (interval < 100 || interval > 100000) { + pr_err("interval_ms must be between 100 and 100000\n"); + return -EINVAL; + } + + return param_set_uint(val, kp); +} + +static const struct kernel_param_ops interval_ms_ops = { + .set = param_set_interval_ms, + .get = param_get_uint, +}; + +module_param_cb(interval_ms, &interval_ms_ops, &sg_ctx.interval_ms, 0444); +MODULE_PARM_DESC(interval_ms, + "Sampling frequency in milliseconds. default: 1000"); + +static int param_set_high_threshold(const char *val, const struct kernel_param *kp) +{ + unsigned int threshold; + int ret; + + ret = kstrtouint(val, 0, &threshold); + if (ret) + return ret; + + if (threshold >= 100 * 100) { + pr_err("high_threshold (%u) can't be more than 99.99%%\n", threshold); + return -EINVAL; + } + + return param_set_uint(val, kp); +} + +static const struct kernel_param_ops high_threshold_ops = { + .set = param_set_high_threshold, + .get = param_get_uint, +}; + +module_param_cb(high_threshold, &high_threshold_ops, &sg_ctx.high_threshold, 0444); +MODULE_PARM_DESC(high_threshold, + "High steal threshold. default: 500 i.e 5%. Must be > low_threshold"); + +module_param_named(low_threshold, sg_ctx.low_threshold, uint, 0444); +MODULE_PARM_DESC(low_threshold, + "Low steal threshold. default: 200 i.e 2%. Must be < high_threshold"); + static int __init steal_governor_init(void) { #ifdef CONFIG_XEN @@ -60,7 +120,16 @@ static int __init steal_governor_init(void) } #endif - pr_info("enabled\n"); + if (sg_ctx.low_threshold >= sg_ctx.high_threshold) { + pr_err("low_threshold (%u) must be less than high_threshold (%u)\n", + sg_ctx.low_threshold, sg_ctx.high_threshold); + return -EINVAL; + } + + sg_ctx.delay = msecs_to_jiffies(sg_ctx.interval_ms); + pr_info("enabled. interval: %ums, high_threshold: %u, low_threshold: %u\n", + sg_ctx.interval_ms, sg_ctx.high_threshold, sg_ctx.low_threshold); + return 0; } -- 2.52.0