On 2017/11/13 18:53, Juergen Gross wrote:
> On 13/11/17 11:06, Quan Xu wrote:
>> From: Quan Xu <[email protected]>
>>
>> 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 <[email protected]>
>> Signed-off-by: Quan Xu <[email protected]>
>> Cc: Juergen Gross <[email protected]>
>> Cc: Alok Kataria <[email protected]>
>> Cc: Rusty Russell <[email protected]>
>> Cc: Thomas Gleixner <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Cc: "H. Peter Anvin" <[email protected]>
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
>> Cc: [email protected]
> Hmm, is the idle entry path really so critical to performance that a new
> pvops function is necessary?
Juergen, Here is the data we get when running benchmark netperf:
1. w/o patch and disable kvm dynamic poll (halt_poll_ns=0):
29031.6 bit/s -- 76.1 %CPU
2. w/ patch and disable kvm dynamic poll (halt_poll_ns=0):
35787.7 bit/s -- 129.4 %CPU
3. w/ kvm dynamic poll:
35735.6 bit/s -- 200.0 %CPU
4. w/patch and w/ kvm dynamic poll:
42225.3 bit/s -- 198.7 %CPU
5. idle=poll
37081.7 bit/s -- 998.1 %CPU
w/ this patch, we will improve performance by 23%.. even we could improve
performance by 45.4%, if we use w/patch and w/ kvm dynamic poll. also the
cost of CPU is much lower than 'idle=poll' case..
> 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.
I assume this feature will be ported to other archs.. a new pvops makes code
clean and easy to maintain. also I tried to add it into existed pvops,
but it
doesn't match.
Quan
Alibaba Cloud
>
> Juergen
>
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