On 2017/11/13 23:08, Ingo Molnar wrote:
* Quan Xu <quan.xu04@xxxxxxxxx> wrote:
From: Quan Xu <quan.xu0@xxxxxxxxx>
To reduce the cost of poll, we introduce three sysctl to control the
poll time when running as a virtual machine with paravirt.
Signed-off-by: Yang Zhang <yang.zhang.wz@xxxxxxxxx>
Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx>
---
Documentation/sysctl/kernel.txt | 35 +++++++++++++++++++++++++++++++++++
arch/x86/kernel/paravirt.c | 4 ++++
include/linux/kernel.h | 6 ++++++
kernel/sysctl.c | 34 ++++++++++++++++++++++++++++++++++
4 files changed, 79 insertions(+), 0 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 694968c..30c25fb 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -714,6 +714,41 @@ kernel tries to allocate a number starting from this one.
==============================================================
+paravirt_poll_grow: (X86 only)
+
+Multiplied value to increase the poll time. This is expected to take
+effect only when running as a virtual machine with CONFIG_PARAVIRT
+enabled. This can't bring any benifit on bare mental even with
+CONFIG_PARAVIRT enabled.
+
+By default this value is 2. Possible values to set are in range {2..16}.
+
+==============================================================
+
+paravirt_poll_shrink: (X86 only)
+
+Divided value to reduce the poll time. This is expected to take effect
+only when running as a virtual machine with CONFIG_PARAVIRT enabled.
+This can't bring any benifit on bare mental even with CONFIG_PARAVIRT
+enabled.
+
+By default this value is 2. Possible values to set are in range {2..16}.
+
+==============================================================
+
+paravirt_poll_threshold_ns: (X86 only)
+
+Controls the maximum poll time before entering real idle path. This is
+expected to take effect only when running as a virtual machine with
+CONFIG_PARAVIRT enabled. This can't bring any benifit on bare mental
+even with CONFIG_PARAVIRT enabled.
+
+By default, this value is 0 means not to poll. Possible values to set
+are in range {0..500000}. Change the value to non-zero if running
+latency-bound workloads in a virtual machine.
I absolutely hate it how this hybrid idle loop polling mechanism is not
self-tuning!
Ingo, actually it is self-tuning..
Please make it all work fine by default, and automatically so, instead of adding
three random parameters...
.. I will make it all fine by default. howerver cloud environment is of
diversity,
could I only leave paravirt_poll_threshold_ns parameter (the maximum
poll time),
which is as similar as "adaptive halt-polling" Wanpeng mentioned.. then
user can turn
it off, or find an appropriate threshold for some odd scenario..
thanks for your comments!!
Quan
Alibaba Cloud
And if it cannot be done automatically then we should rather not do it at all.
Maybe the next submitter of a similar feature can think of a better approach.
Thanks,
Ingo
