Messages in this thread | | | Subject | Re: [PATCH RFC v3 4/6] Documentation: Add three sysctls for smart idle poll | From | Quan Xu <> | Date | Tue, 14 Nov 2017 12:05:16 +0800 |
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On 2017/11/13 23:08, Ingo Molnar wrote: > * Quan Xu <quan.xu04@gmail.com> wrote: > >> From: Quan Xu <quan.xu0@gmail.com> >> >> 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@gmail.com> >> Signed-off-by: Quan Xu <quan.xu0@gmail.com> >> --- >> 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 >
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