summaryrefslogtreecommitdiff
path: root/Documentation/admin-guide
diff options
context:
space:
mode:
authorMing Lei <ming.lei@redhat.com>2020-01-20 12:16:25 +0300
committerThomas Gleixner <tglx@linutronix.de>2020-01-22 18:29:49 +0300
commit11ea68f553e244851d15793a7fa33a97c46d8271 (patch)
treebc31e7e09276cb0e8bd7fa7d89df284023942980 /Documentation/admin-guide
parent099368bb10c0e340f0b236b169e8b13235e0907c (diff)
downloadlinux-11ea68f553e244851d15793a7fa33a97c46d8271.tar.xz
genirq, sched/isolation: Isolate from handling managed interrupts
The affinity of managed interrupts is completely handled in the kernel and cannot be changed via the /proc/irq/* interfaces from user space. As the kernel tries to spread out interrupts evenly accross CPUs on x86 to prevent vector exhaustion, it can happen that a managed interrupt whose affinity mask contains both isolated and housekeeping CPUs is routed to an isolated CPU. As a consequence IO submitted on a housekeeping CPU causes interrupts on the isolated CPU. Add a new sub-parameter 'managed_irq' for 'isolcpus' and the corresponding logic in the interrupt affinity selection code. The subparameter indicates to the interrupt affinity selection logic that it should try to avoid the above scenario. This isolation is best effort and only effective if the automatically assigned interrupt mask of a device queue contains isolated and housekeeping CPUs. If housekeeping CPUs are online then such interrupts are directed to the housekeeping CPU so that IO submitted on the housekeeping CPU cannot disturb the isolated CPU. If a queue's affinity mask contains only isolated CPUs then this parameter has no effect on the interrupt routing decision, though interrupts are only happening when tasks running on those isolated CPUs submit IO. IO submitted on housekeeping CPUs has no influence on those queues. If the affinity mask contains both housekeeping and isolated CPUs, but none of the contained housekeeping CPUs is online, then the interrupt is also routed to an isolated CPU. Interrupts are only delivered when one of the isolated CPUs in the affinity mask submits IO. If one of the contained housekeeping CPUs comes online, the CPU hotplug logic migrates the interrupt automatically back to the upcoming housekeeping CPU. Depending on the type of interrupt controller, this can require that at least one interrupt is delivered to the isolated CPU in order to complete the migration. [ tglx: Removed unused parameter, added and edited comments/documentation and rephrased the changelog so it contains more details. ] Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20200120091625.17912-1-ming.lei@redhat.com
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt26
1 files changed, 24 insertions, 2 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ade4e6ec23e0..765e4274ba71 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1933,9 +1933,31 @@
<cpu number> begins at 0 and the maximum value is
"number of CPUs in system - 1".
- The format of <cpu-list> is described above.
-
+ managed_irq
+
+ Isolate from being targeted by managed interrupts
+ which have an interrupt mask containing isolated
+ CPUs. The affinity of managed interrupts is
+ handled by the kernel and cannot be changed via
+ the /proc/irq/* interfaces.
+
+ This isolation is best effort and only effective
+ if the automatically assigned interrupt mask of a
+ device queue contains isolated and housekeeping
+ CPUs. If housekeeping CPUs are online then such
+ interrupts are directed to the housekeeping CPU
+ so that IO submitted on the housekeeping CPU
+ cannot disturb the isolated CPU.
+
+ If a queue's affinity mask contains only isolated
+ CPUs then this parameter has no effect on the
+ interrupt routing decision, though interrupts are
+ only delivered when tasks running on those
+ isolated CPUs submit IO. IO submitted on
+ housekeeping CPUs has no influence on those
+ queues.
+ The format of <cpu-list> is described above.
iucv= [HW,NET]