From: Peter Maydell <peter.maydell@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "QEMU Developers" <qemu-devel@nongnu.org>,
"Alex Züpke" <alexander.zuepke@hs-rm.de>
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 [thread overview]
Message-ID: <CAFEAcA_zVoBF4pfteyMkS9ObX9uDBbfdK++Ape1_88Ob8zcy1A@mail.gmail.com> (raw)
In-Reply-To: <55844A0A.2070401@redhat.com>
On 19 June 2015 at 17:57, Paolo Bonzini <pbonzini@redhat.com> 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
prev parent reply other threads:[~2015-06-19 17:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-12 16:38 [Qemu-devel] QEMU ARM SMP: IPI delivery delayed until next main loop event // how to improve IPI latency? Alex Züpke
2015-06-12 18:03 ` Peter Maydell
2015-06-15 14:44 ` Alex Züpke
2015-06-15 14:51 ` Peter Maydell
2015-06-15 15:05 ` Alex Züpke
2015-06-15 18:41 ` Peter Maydell
2015-06-15 18:58 ` Peter Maydell
2015-06-15 20:03 ` Alex Zuepke
2015-06-16 10:33 ` Peter Maydell
2015-06-16 10:59 ` Peter Maydell
2015-06-16 11:11 ` Alex Züpke
2015-06-16 11:53 ` Peter Maydell
2015-06-16 12:21 ` Alex Züpke
2015-06-19 15:53 ` Peter Maydell
2015-06-23 7:31 ` Frederic Konrad
2015-06-23 8:09 ` Peter Maydell
2015-06-23 8:33 ` Frederic Konrad
2015-06-23 18:15 ` Peter Maydell
2015-06-25 17:13 ` Peter Maydell
2015-06-15 15:04 ` Peter Maydell
2015-06-15 15:07 ` Alex Züpke
2015-06-15 15:18 ` Peter Maydell
2015-06-15 15:36 ` Alex Züpke
2015-06-15 15:49 ` Peter Maydell
2015-06-15 16:12 ` Alex Züpke
2015-06-15 21:39 ` Peter Crosthwaite
2015-06-19 16:57 ` Paolo Bonzini
2015-06-19 17:25 ` Peter Maydell [this message]
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