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Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastr
From: |
Avi Kivity |
Subject: |
Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2 |
Date: |
Sun, 19 Aug 2007 22:30:00 +0300 |
User-agent: |
Thunderbird 2.0.0.5 (X11/20070719) |
Jamie Lokier wrote:
> Paul Brook wrote:
>
>>> Yes, good thinking, but this should only be done if it actually impacts
>>> something. Reducing overhead from 0.1% to 0.05% is not worthwhile if it
>>> introduces extra complexity.
>>>
>> If the overhead is that small, why are we touching this code in the first
>> place?
>>
>
> Insightful.
>
> A benchmark result was posted which is rather interesting:
>
>
>> address@hidden ~]$ time ./hackbench 50
>> x86_64 host : real 0m10.845s
>> x86_64 host, bound to 1 cpu : real 0m21.884s
>> i386 guest+unix clock : real 0m49.206s
>> i386 guest+hpet clock : real 0m48.292s
>> i386 guest+dynticks clock : real 0m28.835s
>>
>> Results are repeatable and verfied with a stopwatch because I didn't
>> believe them at first :)
>>
>
> I am surprised if 1000 redundant SIGALRMs per second is really causing
> 70% overhead in normal qemu execution, except on a rather old or slow
> machine where signal delivery is very slow.
>
No, something else is happening here. On kvm, a signal is maybe 10us,
to the SIGALRMs represent 1% of overhead. Respectable, but not more.
I suspect that the increased accuracy causes something to behave better
(or just differently). This won't be representative.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
- [Qemu-devel] RE: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure -take2, (continued)
- [Qemu-devel] RE: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure -take2, Dor Laor, 2007/08/19
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/19
- Re: [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Jamie Lokier, 2007/08/19
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/19
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Paul Brook, 2007/08/19
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/19
- RE: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Dor Laor, 2007/08/19
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/20
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Jamie Lokier, 2007/08/19
- RE: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarmtimer infrastrucure - take2, Dor Laor, 2007/08/19
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2,
Avi Kivity <=
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Luca, 2007/08/19
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/19
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Luca Tettamanti, 2007/08/20
- Re: [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, malc, 2007/08/20
- Re: [kvm-devel] [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2, Luca, 2007/08/20
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/21
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Luca Tettamanti, 2007/08/21
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, malc, 2007/08/21
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Avi Kivity, 2007/08/22
- [Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2, Luca Tettamanti, 2007/08/22