From 120881b9e888689cbdb90a1dd1689684d8bc95f3 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Mon, 10 Feb 2020 07:03:06 +0100 Subject: docs: virt: guest-halt-polling.txt convert to ReST Due to some merge conflict, this file ended being alone under Documentation/virtual. The file itself is almost at ReST format. Just minor adjustments are needed: - Adjust title markup; - Adjust a list identation; - add a literal block markup; - Add some blank lines. Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Paolo Bonzini --- Documentation/virtual/guest-halt-polling.txt | 78 ---------------------------- 1 file changed, 78 deletions(-) delete mode 100644 Documentation/virtual/guest-halt-polling.txt (limited to 'Documentation/virtual') diff --git a/Documentation/virtual/guest-halt-polling.txt b/Documentation/virtual/guest-halt-polling.txt deleted file mode 100644 index b3a2a294532d..000000000000 --- a/Documentation/virtual/guest-halt-polling.txt +++ /dev/null @@ -1,78 +0,0 @@ -Guest halt polling -================== - -The cpuidle_haltpoll driver, with the haltpoll governor, allows -the guest vcpus to poll for a specified amount of time before -halting. -This provides the following benefits to host side polling: - - 1) The POLL flag is set while polling is performed, which allows - a remote vCPU to avoid sending an IPI (and the associated - cost of handling the IPI) when performing a wakeup. - - 2) The VM-exit cost can be avoided. - -The downside of guest side polling is that polling is performed -even with other runnable tasks in the host. - -The basic logic as follows: A global value, guest_halt_poll_ns, -is configured by the user, indicating the maximum amount of -time polling is allowed. This value is fixed. - -Each vcpu has an adjustable guest_halt_poll_ns -("per-cpu guest_halt_poll_ns"), which is adjusted by the algorithm -in response to events (explained below). - -Module Parameters -================= - -The haltpoll governor has 5 tunable module parameters: - -1) guest_halt_poll_ns: -Maximum amount of time, in nanoseconds, that polling is -performed before halting. - -Default: 200000 - -2) guest_halt_poll_shrink: -Division factor used to shrink per-cpu guest_halt_poll_ns when -wakeup event occurs after the global guest_halt_poll_ns. - -Default: 2 - -3) guest_halt_poll_grow: -Multiplication factor used to grow per-cpu guest_halt_poll_ns -when event occurs after per-cpu guest_halt_poll_ns -but before global guest_halt_poll_ns. - -Default: 2 - -4) guest_halt_poll_grow_start: -The per-cpu guest_halt_poll_ns eventually reaches zero -in case of an idle system. This value sets the initial -per-cpu guest_halt_poll_ns when growing. This can -be increased from 10000, to avoid misses during the initial -growth stage: - -10k, 20k, 40k, ... (example assumes guest_halt_poll_grow=2). - -Default: 50000 - -5) guest_halt_poll_allow_shrink: - -Bool parameter which allows shrinking. Set to N -to avoid it (per-cpu guest_halt_poll_ns will remain -high once achieves global guest_halt_poll_ns value). - -Default: Y - -The module parameters can be set from the debugfs files in: - - /sys/module/haltpoll/parameters/ - -Further Notes -============= - -- Care should be taken when setting the guest_halt_poll_ns parameter as a -large value has the potential to drive the cpu usage to 100% on a machine which -would be almost entirely idle otherwise. -- cgit