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

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

[Aaron Larson]

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>
---
 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
     }
 }
-- 
2.7.4

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

[David Gibson]

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On Fri, Jun 24, 2016 at 01:18:28PM -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>

As far as I can tell, this is ok.  However, I'd like to get a second
opinion from agraf or BenH before I apply it.

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

[Benjamin Herrenschmidt]

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>

> ---
>  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
>      }
>  }

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

[David Gibson]

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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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