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Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency? |
Date: |
Fri, 19 Jun 2015 18:25:03 +0100 |
On 19 June 2015 at 17:57, Paolo Bonzini <address@hidden> wrote:
>
>
> On 12/06/2015 18:38, Alex Züpke wrote:
>> CPU #0 CPU #1
>> ====== ======
>> ... other stuff ... WFI (wait for interrupt, like x86 "HLT")
>> send SGI in MPCore
>> polls for completeness
>> <time passes ...>
>> polls ...
>> <... and passes ...>
>> still polls ...
>> <... and passes ...>
>> still polls ...
>> <... and passes ...>
>
> Shouldn't CPU#0 do a WFE here? That would work too.
You can do this with SEV/WFE, yes, but you don't have to,
and in fact Linux doesn't currently:
http://lxr.free-electrons.com/source/kernel/smp.c#L108
> Considering that sooner or later we'll have true multithreaded
> emulation, putting a hack doesn't sound like a great prospect.
I'd bet on "later" rather than "sooner", especially if
you want multithreaded on all host architectures.
My not-very-scientific testing of time for a 2xSMP
32-bit Linux guest to boot to userspace shell and
shutdown again suggests it does help: 32.531 secs
vs 34.148 secs. The without-patch version seems more
prone to occasionally stalling so much the boot time
goes up to 45 seconds, too...
-- PMM
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, (continued)
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Peter Maydell, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Alex Züpke, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Peter Maydell, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Alex Züpke, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Peter Maydell, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Alex Züpke, 2015/06/15
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Peter Crosthwaite, 2015/06/15
Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?, Paolo Bonzini, 2015/06/19
- Re: [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency?,
Peter Maydell <=