Re: [Qemu-devel] [PATCH] Adding support for LPD and LPDG instructions

["Éric Bischoff" <ebischoff@suse.com>]

Le mardi 28 février 2017, 06:10:45 CET Richard Henderson a écrit :
> On 02/27/2017 10:22 PM, Eric Bischoff wrote:
> > From: Eric Bischoff <ebischoff@nerim.net>
> > 
> > LPD = LOAD PAIR DISJOINT
> > ---
> > 
> >  target/s390x/insn-data.def |  4 +++-
> >  target/s390x/translate.c   | 21 +++++++++++++++++++++
> >  2 files changed, 24 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target/s390x/insn-data.def b/target/s390x/insn-data.def
> > index 075ff59..e427988 100644
> > --- a/target/s390x/insn-data.def
> > +++ b/target/s390x/insn-data.def
> > @@ -504,7 +504,9 @@
> > 
> >      C(0xb9e2, LOCGR,   RRF_c, LOC, r1, r2, r1, 0, loc, 0)
> >      C(0xebf2, LOC,     RSY_b, LOC, r1, m2_32u, new, r1_32, loc, 0)
> >      C(0xebe2, LOCG,    RSY_b, LOC, r1, m2_64, r1, 0, loc, 0)
> > 
> > -/* LOAD PAIR DISJOINT TODO */
> > +/* LOAD PAIR DISJOINT */
> > +    C(0xc804, LPD,     SSF,   ILA, m1_32s, m2_32s, 0, r3_P32, movx, zero)
> > +    C(0xc805, LPDG,    SSF,   ILA, m1_64, m2_64, 0, r3_P64, movx, zero)
> 
> The think is, in order to be able to say that the two loads were
> interlocked, which is what you're doing with CC=0, we need to provide some
> atomicity.
> 
> In general, this is going to require that you check parallel_cpus, and if
> true, signal cpu_loop_exit_atomic.
> 
> As a special case, it would be possible to check for two loads that happen
> to be sequential and perform them as an atomic read.  Whether that happens
> often enough to be worthwhile I don't know.

Understood now.

I'm working on a v3 patch based on the code kindly sent in private mail by 
Richard.


-- 
Eric Bischoff - SUSE Manager QA Engineer
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Jennifer Guild, Dilip 
Upmanyu, Graham Norton, HRB 21284 (AG Nürnberg)