From 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 27 Apr 2024 12:05:51 +0200 Subject: Adding upstream version 5.10.209. Signed-off-by: Daniel Baumann --- Documentation/core-api/irq/irq-affinity.rst | 70 +++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) create mode 100644 Documentation/core-api/irq/irq-affinity.rst (limited to 'Documentation/core-api/irq/irq-affinity.rst') diff --git a/Documentation/core-api/irq/irq-affinity.rst b/Documentation/core-api/irq/irq-affinity.rst new file mode 100644 index 000000000..29da50008 --- /dev/null +++ b/Documentation/core-api/irq/irq-affinity.rst @@ -0,0 +1,70 @@ +================ +SMP IRQ affinity +================ + +ChangeLog: + - Started by Ingo Molnar + - Update by Max Krasnyansky + + +/proc/irq/IRQ#/smp_affinity and /proc/irq/IRQ#/smp_affinity_list specify +which target CPUs are permitted for a given IRQ source. It's a bitmask +(smp_affinity) or cpu list (smp_affinity_list) of allowed CPUs. It's not +allowed to turn off all CPUs, and if an IRQ controller does not support +IRQ affinity then the value will not change from the default of all cpus. + +/proc/irq/default_smp_affinity specifies default affinity mask that applies +to all non-active IRQs. Once IRQ is allocated/activated its affinity bitmask +will be set to the default mask. It can then be changed as described above. +Default mask is 0xffffffff. + +Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting +it to CPU4-7 (this is an 8-CPU SMP box):: + + [root@moon 44]# cd /proc/irq/44 + [root@moon 44]# cat smp_affinity + ffffffff + + [root@moon 44]# echo 0f > smp_affinity + [root@moon 44]# cat smp_affinity + 0000000f + [root@moon 44]# ping -f h + PING hell (195.4.7.3): 56 data bytes + ... + --- hell ping statistics --- + 6029 packets transmitted, 6027 packets received, 0% packet loss + round-trip min/avg/max = 0.1/0.1/0.4 ms + [root@moon 44]# cat /proc/interrupts | grep 'CPU\|44:' + CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 + 44: 1068 1785 1785 1783 0 0 0 0 IO-APIC-level eth1 + +As can be seen from the line above IRQ44 was delivered only to the first four +processors (0-3). +Now lets restrict that IRQ to CPU(4-7). + +:: + + [root@moon 44]# echo f0 > smp_affinity + [root@moon 44]# cat smp_affinity + 000000f0 + [root@moon 44]# ping -f h + PING hell (195.4.7.3): 56 data bytes + .. + --- hell ping statistics --- + 2779 packets transmitted, 2777 packets received, 0% packet loss + round-trip min/avg/max = 0.1/0.5/585.4 ms + [root@moon 44]# cat /proc/interrupts | 'CPU\|44:' + CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7 + 44: 1068 1785 1785 1783 1784 1069 1070 1069 IO-APIC-level eth1 + +This time around IRQ44 was delivered only to the last four processors. +i.e counters for the CPU0-3 did not change. + +Here is an example of limiting that same irq (44) to cpus 1024 to 1031:: + + [root@moon 44]# echo 1024-1031 > smp_affinity_list + [root@moon 44]# cat smp_affinity_list + 1024-1031 + +Note that to do this with a bitmask would require 32 bitmasks of zero +to follow the pertinent one. -- cgit v1.2.3