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Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC v1 0/3] Enable MTTCG on PPC64

From: Benjamin Herrenschmidt
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC v1 0/3] Enable MTTCG on PPC64
Date: Tue, 11 Apr 2017 23:26:07 +1000

On Tue, 2017-04-11 at 14:28 +0200, Cédric Le Goater wrote:
> I really don't know. 
> Ben, now that we have mttcg activated by default on ppc, it takes 
> a while for the linux kernel to do the early setup. I think we are
> in the code section where we spin loop the secondaries. Most of the
> time is spent in skiboot under cpu_idle/relax.
> Any idea where that could come from ? 
> > See c22edfebff29f63d793032e4fbd42a035bb73e27 for an example.
> Thanks for the hint.

They are spinning, but they have smt_low instructions in the loop,
maybe that causes us to do some kind of synchronization as we exit
the emulation loop on these ? I added that to force relinguish time
to other threads on the pre-MT TCG...

There isn't really such a "pause" instruction. At least not yet.... P9
has a wait that is meant to wait for special AS_Notify cycles but will
also wait for interrupts. We don't have an mwait at this point.


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