Messages in this thread Patch in this message | | | From | Chen Yu <> | Subject | [RFC PATCH] genirq: Exclude managed irq during irq migration | Date | Fri, 20 Oct 2023 15:25:22 +0800 |
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The managed IRQ will be shutdown and not be migrated to other CPUs during CPU offline. Later when the CPU is online, the managed IRQ will be re-enabled on this CPU. The managed IRQ can be used to reduce the IRQ migration during CPU hotplug.
Before putting the CPU offline, the number of the already allocated IRQs on this offlining CPU will be compared to the total number of available IRQ vectors on the remaining online CPUs. If there is not enough slot for these IRQs to be migrated to, the CPU offline will be terminated. However, currently the code treats the managed IRQ as migratable, which is not true, and brings false negative during CPU hotplug and hibernation stress test.
For example:
cat /sys/kernel/debug/irq/domains/VECTOR
name: VECTOR size: 0 mapped: 338 flags: 0x00000103 Online bitmaps: 168 Global available: 33009 Global reserved: 83 Total allocated: 255 <------ System: 43: 0-21,50,128,192,233-236,240-242,244,246-255 | CPU | avl | man | mac | act | vectors 0 180 1 1 18 32-49 1 196 1 1 2 32-33 ... 166 197 1 1 1 32 167 197 1 1 1 32
//put CPU167 offline pepc.standalone cpu-hotplug offline --cpus 167
cat /sys/kernel/debug/irq/domains/VECTOR
name: VECTOR size: 0 mapped: 338 flags: 0x00000103 Online bitmaps: 167 Global available: 32812 Global reserved: 83 Total allocated: 254 <------ System: 43: 0-21,50,128,192,233-236,240-242,244,246-255 | CPU | avl | man | mac | act | vectors 0 180 1 1 18 32-49 1 196 1 1 2 32-33 ... 166 197 1 1 1 32
After CPU167 is offline, the number of allocated vectors decreases from 255 to 254. Since the only IRQ on CPU167 is managed(mac field), it is not migrated. But the current code thinks that there is 1 IRQ to be migrated.
Fix the check by substracting the number of managed IRQ from allocated one.
Fixes: 2f75d9e1c905 ("genirq: Implement bitmap matrix allocator") Reported-by: Wendy Wang <wendy.wang@intel.com> Signed-off-by: Chen Yu <yu.c.chen@intel.com> --- kernel/irq/matrix.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/irq/matrix.c b/kernel/irq/matrix.c index 1698e77645ac..d245ad76661e 100644 --- a/kernel/irq/matrix.c +++ b/kernel/irq/matrix.c @@ -475,7 +475,7 @@ unsigned int irq_matrix_allocated(struct irq_matrix *m) { struct cpumap *cm = this_cpu_ptr(m->maps); - return cm->allocated; + return cm->allocated - cm->managed_allocated; } #ifdef CONFIG_GENERIC_IRQ_DEBUGFS -- 2.25.1
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