view Documentation/IRQ-affinity.txt @ 897:329ea0ccb344

balloon: try harder to balloon up under memory pressure.

Currently if the balloon driver is unable to increase the guest's
reservation it assumes the failure was due to reaching its full
allocation, gives up on the ballooning operation and records the limit
it reached as the "hard limit". The driver will not try again until
the target is set again (even to the same value).

However it is possible that ballooning has in fact failed due to
memory pressure in the host and therefore it is desirable to keep
attempting to reach the target in case memory becomes available. The
most likely scenario is that some guests are ballooning down while
others are ballooning up and therefore there is temporary memory
pressure while things stabilise. You would not expect a well behaved
toolstack to ask a domain to balloon to more than its allocation nor
would you expect it to deliberately over-commit memory by setting
balloon targets which exceed the total host memory.

This patch drops the concept of a hard limit and causes the balloon
driver to retry increasing the reservation on a timer in the same
manner as when decreasing the reservation.

Also if we partially succeed in increasing the reservation
(i.e. receive less pages than we asked for) then we may as well keep
those pages rather than returning them to Xen.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Fri Jun 05 14:01:20 2009 +0100 (2009-06-05)
parents 831230e53067
line source
2 SMP IRQ affinity, started by Ingo Molnar <mingo@redhat.com>
5 /proc/irq/IRQ#/smp_affinity specifies which target CPUs are permitted
6 for a given IRQ source. It's a bitmask of allowed CPUs. It's not allowed
7 to turn off all CPUs, and if an IRQ controller does not support IRQ
8 affinity then the value will not change from the default 0xffffffff.
10 Here is an example of restricting IRQ44 (eth1) to CPU0-3 then restricting
11 the IRQ to CPU4-7 (this is an 8-CPU SMP box):
13 [root@moon 44]# cat smp_affinity
14 ffffffff
15 [root@moon 44]# echo 0f > smp_affinity
16 [root@moon 44]# cat smp_affinity
17 0000000f
18 [root@moon 44]# ping -f h
19 PING hell ( 56 data bytes
20 ...
21 --- hell ping statistics ---
22 6029 packets transmitted, 6027 packets received, 0% packet loss
23 round-trip min/avg/max = 0.1/0.1/0.4 ms
24 [root@moon 44]# cat /proc/interrupts | grep 44:
25 44: 0 1785 1785 1783 1783 1
26 1 0 IO-APIC-level eth1
27 [root@moon 44]# echo f0 > smp_affinity
28 [root@moon 44]# ping -f h
29 PING hell ( 56 data bytes
30 ..
31 --- hell ping statistics ---
32 2779 packets transmitted, 2777 packets received, 0% packet loss
33 round-trip min/avg/max = 0.1/0.5/585.4 ms
34 [root@moon 44]# cat /proc/interrupts | grep 44:
35 44: 1068 1785 1785 1784 1784 1069 1070 1069 IO-APIC-level eth1
36 [root@moon 44]#