Re: [Qemu-devel] [Qemu-ppc] [PATCH] target-ppc: gen_pause for instructions: yield, mdoio, mdoom, miso

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Jun 29, 2016 at 10:00:57PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2016-06-24 at 13:18 -0700, Aaron Larson wrote:
> > Call gen_pause for all "or rx,rx,rx" encodings other nop.  This
> > provides a reasonable implementation for yield, and a better
> > approximation for mdoio, mdoom, and miso.  The choice to pause for
> > all
> > encodings !=0 leverages the PowerISA admonition that the reserved
> > encodings might change program priority, providing a slight "future
> > proofing".
> > 
> > Signed-off-by: Aaron Larson <alarson@ddci.com>
> 
> Acked-by: Benjamin Herrenschmidt <benh@kerne.crashing.org>

Applied to ppc-for-2.7, thanks.

> > ---
> >  target-ppc/translate.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> > index 2f1c591..c4559b6 100644
> > --- a/target-ppc/translate.c
> > +++ b/target-ppc/translate.c
> > @@ -1471,7 +1471,7 @@ static void gen_or(DisasContext *ctx)
> >      } else if (unlikely(Rc(ctx->opcode) != 0)) {
> >          gen_set_Rc0(ctx, cpu_gpr[rs]);
> >  #if defined(TARGET_PPC64)
> > -    } else {
> > +    } else if (rs != 0) { /* 0 is nop */
> >          int prio = 0;
> >  
> >          switch (rs) {
> > @@ -1514,7 +1514,6 @@ static void gen_or(DisasContext *ctx)
> >              break;
> >  #endif
> >          default:
> > -            /* nop */
> >              break;
> >          }
> >          if (prio) {
> > @@ -1524,13 +1523,15 @@ static void gen_or(DisasContext *ctx)
> >              tcg_gen_ori_tl(t0, t0, ((uint64_t)prio) << 50);
> >              gen_store_spr(SPR_PPR, t0);
> >              tcg_temp_free(t0);
> > -            /* Pause us out of TCG otherwise spin loops with smt_low
> > -             * eat too much CPU and the kernel hangs
> > -             */
> > +        }
> >  #if !defined(CONFIG_USER_ONLY)
> > -            gen_pause(ctx);
> > +        /* Pause out of TCG otherwise spin loops with smt_low eat
> > too much
> > +         * CPU and the kernel hangs.  This applies to all encodings
> > other
> > +         * than no-op, e.g., miso(rs=26), yield(27), mdoio(29),
> > mdoom(30),
> > +         * and all currently undefined.
> > +         */
> > +        gen_pause(ctx);
> >  #endif
> > -        }
> >  #endif
> >      }
> >  }
> 

-- 
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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