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Tue, 7 Apr 2026 19:50:01 +0000 (GMT) Message-ID: <8beafb01-f891-4b13-8eae-c6f3face7001@linux.ibm.com> Date: Wed, 8 Apr 2026 01:20:01 +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 v2 00/17] sched/paravirt: Introduce cpu_preferred_mask and steal-driven vCPU backoff To: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, yury.norov@gmail.com, gregkh@linuxfoundation.org Cc: 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, mgorman@suse.de, bsegall@google.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, joelagnelf@nvidia.com References: <20260407191950.643549-1-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260407191950.643549-1-sshegde@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDA3MDE4MCBTYWx0ZWRfX9LvO7xJ7wT/V 52qQbTCEK+g20bBHmuUFMW3yxDPVv8aTFHjEVEEzvi3uzGffa77S1cPQaTbWRdjxD/MlDHbX8sS hWJNmELD+mCzmkNVZDAMnfvlXfA8DYWI68WekOoJDUQsYXL6tq3Fwo3Xlf9EBLhr/BM6FnwBcHU d6tNf1PcgUt77Vv438QWqh0WCEa2WFjtblsrI1rXZRG8On/9MiKHqGeuF2Eq8lxEz3/xibFsqdS IPJmvqjpkzvibnNLE0pFiH60o29Aecr4u+pRbcWAEszf1A7KMk3gWmP6vlUnJMsHC0i8qHvWJ3y /pJiQ+2syOETDsa7SxyJcmxTI4BdsYp2dyppEE/pQLZNKe95TaogusN6OcoQlQk2eG+/tY3/WBP dhLCGtoVxp0DGyqrHf1CkT1C6XVjlTMj6htHeY2xl50h7w4NvKE7TTwssvXsEd9jEiW40X9tZfw n2Q0YGmyjLIyn6QzCRA== X-Proofpoint-ORIG-GUID: C1M5F8BC-dJ-0N1Be_HE0gRN81xNw49Q X-Authority-Analysis: v=2.4 cv=e9k2j6p/ c=1 sm=1 tr=0 ts=69d55ff3 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=Bz-2Z5wCdpiZ_NuuUJcA:9 a=+jEqtf1s3R9VXZ0wqowq2kgwd+I=:19 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Io3LkrPkXsTtHW_HA04is_OYOP1W9T2Y X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-07_04,2026-04-07_05,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 malwarescore=0 suspectscore=0 spamscore=0 bulkscore=0 adultscore=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604070180 > I will attach the irqbalance patch which detects the changes in this > mask and re-adjusts the irq affinities. Series doesn't address when > irqbalance=n. Assuming many distros have irqbalance=y by default. > Subject: [PATCH] irqbalance: Check for changes in cpu_preferred_mask --- cputree.c | 28 +++++++++++++++++++++++++++- irqbalance.c | 2 ++ irqbalance.h | 1 + 3 files changed, 30 insertions(+), 1 deletion(-) diff --git a/cputree.c b/cputree.c index 9baa264..1db3422 100644 --- a/cputree.c +++ b/cputree.c @@ -56,6 +56,11 @@ cpumask_t banned_cpus; cpumask_t cpu_online_map; +/* This can dynamically change. If any change in mask detect + * and trigger a rebuild + */ +cpumask_t cpu_preferred_mask; + /* it's convenient to have the complement of banned_cpus available so that the AND operator can be used to mask out unwanted cpus @@ -506,15 +511,36 @@ void clear_work_stats(void) for_each_object(numa_nodes, clear_obj_stats, NULL); } +void parse_preferred_cpus(void) +{ + cpumask_t preferred; + char *path = NULL; + + path = "/sys/devices/system/cpu/preferred"; + cpus_clear(preferred); + process_one_line(path, get_mask_from_cpulist, &preferred); + + /* Did anything change compared to earlier */ + if (!cpus_equal(preferred, cpu_preferred_mask)) { + log(TO_CONSOLE, LOG_INFO, "cpu preferred mask changed\n"); + need_rebuild = 1; + } + + cpus_copy(cpu_preferred_mask, preferred); +} void parse_cpu_tree(void) { DIR *dir; struct dirent *entry; + char buffer[4096]; setup_banned_cpus(); - cpus_complement(unbanned_cpus, banned_cpus); + cpus_andnot(unbanned_cpus, cpu_preferred_mask, banned_cpus); + + cpumask_scnprintf(buffer, 4096, unbanned_cpus); + log(TO_CONSOLE, LOG_INFO, "Unbanned CPUs: %s\n", buffer); dir = opendir("/sys/devices/system/cpu"); if (!dir) diff --git a/irqbalance.c b/irqbalance.c index f80244c..f3d46b8 100644 --- a/irqbalance.c +++ b/irqbalance.c @@ -229,6 +229,7 @@ static void parse_command_line(int argc, char **argv) static void build_object_tree(void) { build_numa_node_list(); + parse_preferred_cpus(); parse_cpu_tree(); rebuild_irq_db(); } @@ -275,6 +276,7 @@ gboolean scan(gpointer data __attribute__((unused))) log(TO_CONSOLE, LOG_INFO, "\n\n\n-----------------------------------------------------------------------------\n"); clear_work_stats(); parse_proc_interrupts(); + parse_preferred_cpus(); /* cope with cpu hotplug -- detected during /proc/interrupts parsing */ diff --git a/irqbalance.h b/irqbalance.h index 47e40cc..593b183 100644 --- a/irqbalance.h +++ b/irqbalance.h @@ -57,6 +57,7 @@ void migrate_irq_obj(struct topo_obj *from, struct topo_obj *to, struct irq_info void activate_mappings(void); void clear_cpu_tree(void); void free_cpu_topo(gpointer data); +extern void parse_preferred_cpus(void); /*===================NEW BALANCER FUNCTIONS============================*/ /* -- 2.47.3