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SubjectRe: [PATCH RFC v3 1/6] x86/paravirt: Add pv_idle_ops to paravirt ops
2017-11-13 18:53 GMT+08:00 Juergen Gross <>:
> On 13/11/17 11:06, Quan Xu wrote:
>> From: Quan Xu <>
>> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called
>> in idle path which will poll 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 from the vmexit which is a hardware
>> context switch between virtual machine 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 <>
>> Signed-off-by: Quan Xu <>
>> Cc: Juergen Gross <>
>> Cc: Alok Kataria <>
>> Cc: Rusty Russell <>
>> Cc: Thomas Gleixner <>
>> Cc: Ingo Molnar <>
>> Cc: "H. Peter Anvin" <>
>> Cc:
>> Cc:
>> Cc:
>> Cc:
> Hmm, is the idle entry path really so critical to performance that a new
> pvops function is necessary? Wouldn't a function pointer, maybe guarded
> by a static key, be enough? A further advantage would be that this would
> work on other architectures, too.

There is a "Adaptive halt-polling" which are merged to upstream more
than two years ago avoids to thread the critical path and has already
been ported to other architectures.

Wanpeng Li

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