@@ -2460,28 +2460,30 @@
"number of CPUs in system - 1".
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.
+ Isolate CPUs from IRQ-related work for drivers
+ that support managed interrupts, ensuring no
+ IRQ work is scheduled on the isolated CPUs. The
+ kernel manages the affinity of managed
+ interrupts, which cannot be changed via the
+ /proc/irq/* interfaces.
+
+ Since isolated CPUs do not handle IRQ work, the
+ work is forwarded to housekeeping CPUs.
+ Housekeeping and isolated CPUs are grouped into
+ sets, ensuring at least one housekeeping CPU is
+ available per set. Consequently, if all
+ housekeeping CPUs in a set are offlined, there
+ will be no CPU available to handle IRQ work for
+ the isolated CPUs. Therefore, users should
+ offline all isolated CPUs before offlining the
+ housekeeping CPUs in a set to avoid stalls.
+
+ The block layer ensures that no I/O is
+ scheduled on isolated CPU, except when user
+ applications running on the isolated CPUs issue
+ I/O requests. In this case the I/O is issued
+ from the isolated CPU and the IRQ related work
+ is forwared to a housekeeping CPU.
The format of <cpu-list> is described above.
The managed_irq documentation is a bit difficult to understand. Rephrase the current text and add the latest changes how managed_irq CPU sets are handled. Isolated CPUs and housekeeping CPUs are grouped into sets and the possibility of stalls if all housekeeping CPUs are offlined in a set. Signed-off-by: Daniel Wagner <wagi@kernel.org> --- Documentation/admin-guide/kernel-parameters.txt | 46 +++++++++++++------------ 1 file changed, 24 insertions(+), 22 deletions(-)