Re: [Qemu-devel] [PATCH RFC 0/4] Enable MTTCG on PowerPC

[David Gibson]

On Fri, Sep 02, 2016 at 05:19:21PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2016-09-02 at 12:02 +0530, Nikunj A Dadhania wrote:
> > The series is a first attempt at enabling Multi-Threaded TCG on PowerPC.
> > Changes that were needed to enable PowerPC are pretty simple;
> > 
> > Patch 01: Take a iothread lock during hcall, as hcall can generate io 
> > requests
> >       02: For TCG, we were harcoding smt as 1, this gets rid of the 
> > limitation
> 
> If we do this, we need to implement the shared SPRs properly and the
> inter-thread doorbells...

Exactly.  I think we want to get MTTCG working with multiple emulated
cores first, then look into handling emulated hardware
multi-threading.  2/4 suggests you are conflating the two, when
they're really not related AFAICT.

> 
> >       03: Use atomic_cmpxchg in store conditional
> >       04: With more threads, flush the entry from each cpu. 
> >       This can be optimized further.
> > 
> > The patches are based on the Alex Bennee's base enabling patches for 
> > MTTCG[1] and Emilios's cmpxchg atomics. The consolidated tree of the 
> > above patches is here:
> > 
> > https://github.com/stsquad/qemu/tree/mttcg/base-patches-v4-with-cmpxchg-atomics-v2
> > 
> > Apart from the above, PPC patches are based out of ppc-for-2.8 and 
> > load/store consolidation patches [2]
> > 
> > Series with all dependent patches available here: 
> > https://github.com/nikunjad/qemu/tree/ppc_mttcg_v1
> > 
> > Testing: 
> > ========
> > 
> > -smp 4,cores=1,threads=4 -accel tcg,thread=multi
> > 
> > TODO
> > ====
> > Implement msgsndp instructions(door-bell), newer kernels enable it 
> > depending on the PVR. I have been using following workaround to boot.
> > https://github.com/nikunjad/qemu/commit/2c10052c5f93418a6b920e6ba3ce1813fcf50bc4
> > 
> > [1] https://www.mail-archive.com/address@hidden/msg391966.html
> > [2] https://lists.gnu.org/archive/html/qemu-ppc/2016-08/msg00265.html
> > 
> > Nikunj A Dadhania (4):
> >   spapr-hcall: take iothread lock during handler call
> >   target-ppc: with MTTCG report more threads
> >   target-ppc: use atomic_cmpxchg for ld/st reservation
> >   target-ppc: flush tlb from all the cpu
> > 
> >  cputlb.c                | 15 +++++++++++++++
> >  hw/ppc/spapr_hcall.c    | 11 +++++++++--
> >  include/exec/exec-all.h |  2 ++
> >  target-ppc/kvm.c        |  2 +-
> >  target-ppc/kvm_ppc.h    |  2 +-
> >  target-ppc/mmu-hash64.c |  2 +-
> >  target-ppc/translate.c  | 24 +++++++++++++++++++++---
> >  7 files changed, 50 insertions(+), 8 deletions(-)
> > 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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