Re: [Xen-devel] [RFC PATCH v2 1/7] x86/paravirt: Add pv_idle_ops to paravirt ops

[Juergen Gross <jgross@xxxxxxxx>]

On 29/08/17 15:55, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 29, 2017 at 11:46:35AM +0000, Yang Zhang wrote:
>> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called in
>> idle path which will polling for a while before we enter the real idle
>> state.
>>
>> In virtualization, idle path includes several heavy operations
>> includes timer access(LAPIC timer or TSC deadline timer) which will hurt
>> performance especially for latency intensive workload like message
>> passing task. The cost is mainly come from the vmexit which is a
>> hardware context switch between VM and hypervisor. Our solution is to
>> poll for a while and do not enter real idle path if we can get the
>> schedule event during polling.
>>
>> Poll may cause the CPU waste so we adopt a smart polling mechanism to
>> reduce the useless poll.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@xxxxxxxxx>
>> Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx>
>> Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
>> Cc: Chris Wright <chrisw@xxxxxxxxxxxx>
>> Cc: Alok Kataria <akataria@xxxxxxxxxx>
>> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> Cc: x86@xxxxxxxxxx
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Cc: Pan Xinhui <xinhui.pan@xxxxxxxxxxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
>> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> Adding xen-devel.
> 
> Juergen, we really should replace Jeremy's name with xen-devel or
> your name..

I wouldn't mind being added. What does Jeremy think of being removed?

> Wasn't there an patch by you that took some of the 
> mainternship over it?

I added include/linux/hypervisor.h to the PARAVIRT section and offered
to maintain it in case the PARAVIRT maintainers didn't want to.


Juergen

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