[PATCH 0/1] Add Zihintpause support

[PATCH 0/1] Add Zihintpause support

[Dao Lu]

This patch adds RISC-V Zihintpause support. The extension is set to be enabled
by default and opcode has been added to insn32.decode.

Added trans_pause for TCG to mainly be a no-op and break reservation.

The change can also be found in:
https://github.com/dlu42/qemu/tree/zihintpause_support_v1

Tested along with pause support added to cpu_relax function for linux, the
changes I made to linux to test can be found here:
https://github.com/dlu42/linux/tree/pause_support_v1

Dao Lu (1):
  Add Zihintpause support

 target/riscv/cpu.c                      |  2 ++
 target/riscv/cpu.h                      |  1 +
 target/riscv/insn32.decode              |  7 ++++++-
 target/riscv/insn_trans/trans_rvi.c.inc | 18 ++++++++++++++++++
 4 files changed, 27 insertions(+), 1 deletion(-)

-- 
2.36.0

[PATCH 1/1] Add Zihintpause support

[Dao Lu]

Added support for RISC-V PAUSE instruction from Zihintpause extension, enabeld
by default.

Signed-off-by: Dao Lu <daolu@rivosinc.com>
---
 target/riscv/cpu.c                      |  2 ++
 target/riscv/cpu.h                      |  1 +
 target/riscv/insn32.decode              |  7 ++++++-
 target/riscv/insn_trans/trans_rvi.c.inc | 18 ++++++++++++++++++
 4 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ccacdee215..183fb37fdf 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -825,6 +825,7 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("Counters", RISCVCPU, cfg.ext_counters, true),
     DEFINE_PROP_BOOL("Zifencei", RISCVCPU, cfg.ext_ifencei, true),
     DEFINE_PROP_BOOL("Zicsr", RISCVCPU, cfg.ext_icsr, true),
+    DEFINE_PROP_BOOL("Zihintpause", RISCVCPU, cfg.ext_zihintpause, true),
     DEFINE_PROP_BOOL("Zfh", RISCVCPU, cfg.ext_zfh, false),
     DEFINE_PROP_BOOL("Zfhmin", RISCVCPU, cfg.ext_zfhmin, false),
     DEFINE_PROP_BOOL("Zve32f", RISCVCPU, cfg.ext_zve32f, false),
@@ -996,6 +997,7 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int max_str_len)
      *    extensions by an underscore.
      */
     struct isa_ext_data isa_edata_arr[] = {
+        ISA_EDATA_ENTRY(zihintpause, ext_zihintpause),
         ISA_EDATA_ENTRY(zfh, ext_zfh),
         ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
         ISA_EDATA_ENTRY(zfinx, ext_zfinx),
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index fe6c9a2c92..e466a04a59 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -394,6 +394,7 @@ struct RISCVCPUConfig {
     bool ext_counters;
     bool ext_ifencei;
     bool ext_icsr;
+    bool ext_zihintpause;
     bool ext_svinval;
     bool ext_svnapot;
     bool ext_svpbmt;
diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 4033565393..595fdcdad8 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -149,7 +149,12 @@ srl      0000000 .....    ..... 101 ..... 0110011 @r
 sra      0100000 .....    ..... 101 ..... 0110011 @r
 or       0000000 .....    ..... 110 ..... 0110011 @r
 and      0000000 .....    ..... 111 ..... 0110011 @r
-fence    ---- pred:4 succ:4 ----- 000 ----- 0001111
+
+{
+  pause  0000 0001   0000   00000 000 00000 0001111
+  fence  ---- pred:4 succ:4 ----- 000 ----- 0001111
+}
+
 fence_i  ---- ----   ----   ----- 001 ----- 0001111
 csrrw    ............     ..... 001 ..... 1110011 @csr
 csrrs    ............     ..... 010 ..... 1110011 @csr
diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
index f1342f30f8..528c30c9a2 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -18,6 +18,12 @@
  * this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#define REQUIRE_ZIHINTPAUSE(ctx) do { \
+    if (!ctx->cfg_ptr->ext_zihintpause) {      \
+        return false;         \
+    }                         \
+} while (0)
+
 static bool trans_illegal(DisasContext *ctx, arg_empty *a)
 {
     gen_exception_illegal(ctx);
@@ -796,6 +802,18 @@ static bool trans_srad(DisasContext *ctx, arg_srad *a)
     return gen_shift(ctx, a, EXT_SIGN, tcg_gen_sar_tl, NULL);
 }
 
+static bool trans_pause(DisasContext *ctx, arg_pause *a)
+{
+    REQUIRE_ZIHINTPAUSE(ctx);
+
+    /*
+     * PAUSE is a no-op in QEMU,
+     * however we need to clear the reservation
+     */
+    tcg_gen_movi_tl(load_res, -1);
+
+    return true;
+}
 
 static bool trans_fence(DisasContext *ctx, arg_fence *a)
 {
-- 
2.36.0

Re: [PATCH 1/1] Add Zihintpause support

[Richard Henderson]

On 5/9/22 23:42, Dao Lu wrote:
> +static bool trans_pause(DisasContext *ctx, arg_pause *a)
> +{
> +    REQUIRE_ZIHINTPAUSE(ctx);
> +
> +    /*
> +     * PAUSE is a no-op in QEMU,
> +     * however we need to clear the reservation
> +     */
> +    tcg_gen_movi_tl(load_res, -1);

I recommend ending the TB and returning to the main loop.  When running in round-robin 
mode, this will yield to the next cpu.


r~

Re: [PATCH 1/1] Add Zihintpause support

[Dao Lu]

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Thanks Richard! I have fixed it following your advice:

diff --git a/target/riscv/insn_trans/trans_rvi.c.inc
b/target/riscv/insn_trans/trans_rvi.c.inc
index 528c30c9a2..acd2548e9b 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -808,9 +808,13 @@ static bool trans_pause(DisasContext *ctx, arg_pause
*a)

     /*
      * PAUSE is a no-op in QEMU,
-     * however we need to clear the reservation
+     * however we need to clear the reservation,
+     * end the TB and return to main loop
      */
     tcg_gen_movi_tl(load_res, -1);
+    gen_set_pc_imm(ctx, ctx->pc_succ_insn);
+    tcg_gen_exit_tb(NULL, 0);
+    ctx->base.is_jmp = DISAS_NORETURN;

     return true;
 }

I will wait a bit to see if there are any more comments.

On Tue, May 10, 2022 at 8:43 AM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 5/9/22 23:42, Dao Lu wrote:
> > +static bool trans_pause(DisasContext *ctx, arg_pause *a)
> > +{
> > +    REQUIRE_ZIHINTPAUSE(ctx);
> > +
> > +    /*
> > +     * PAUSE is a no-op in QEMU,
> > +     * however we need to clear the reservation
> > +     */
> > +    tcg_gen_movi_tl(load_res, -1);
>
> I recommend ending the TB and returning to the main loop.  When running in
> round-robin
> mode, this will yield to the next cpu.
>
>
> r~
>

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Re: [PATCH 1/1] Add Zihintpause support

[Heiko Stübner]

Am Dienstag, 10. Mai 2022, 08:42:31 CEST schrieb Dao Lu:
> Added support for RISC-V PAUSE instruction from Zihintpause extension, enabeld
> by default.
> 
> Signed-off-by: Dao Lu <daolu@rivosinc.com>

This patch with your fixup applied to it and of course
a matching kernel:

Tested-by: Heiko Stuebner <heiko@sntech.de>


> ---
>  target/riscv/cpu.c                      |  2 ++
>  target/riscv/cpu.h                      |  1 +
>  target/riscv/insn32.decode              |  7 ++++++-
>  target/riscv/insn_trans/trans_rvi.c.inc | 18 ++++++++++++++++++
>  4 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ccacdee215..183fb37fdf 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -825,6 +825,7 @@ static Property riscv_cpu_properties[] = {
>      DEFINE_PROP_BOOL("Counters", RISCVCPU, cfg.ext_counters, true),
>      DEFINE_PROP_BOOL("Zifencei", RISCVCPU, cfg.ext_ifencei, true),
>      DEFINE_PROP_BOOL("Zicsr", RISCVCPU, cfg.ext_icsr, true),
> +    DEFINE_PROP_BOOL("Zihintpause", RISCVCPU, cfg.ext_zihintpause, true),
>      DEFINE_PROP_BOOL("Zfh", RISCVCPU, cfg.ext_zfh, false),
>      DEFINE_PROP_BOOL("Zfhmin", RISCVCPU, cfg.ext_zfhmin, false),
>      DEFINE_PROP_BOOL("Zve32f", RISCVCPU, cfg.ext_zve32f, false),
> @@ -996,6 +997,7 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int max_str_len)
>       *    extensions by an underscore.
>       */
>      struct isa_ext_data isa_edata_arr[] = {
> +        ISA_EDATA_ENTRY(zihintpause, ext_zihintpause),
>          ISA_EDATA_ENTRY(zfh, ext_zfh),
>          ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
>          ISA_EDATA_ENTRY(zfinx, ext_zfinx),
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index fe6c9a2c92..e466a04a59 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -394,6 +394,7 @@ struct RISCVCPUConfig {
>      bool ext_counters;
>      bool ext_ifencei;
>      bool ext_icsr;
> +    bool ext_zihintpause;
>      bool ext_svinval;
>      bool ext_svnapot;
>      bool ext_svpbmt;
> diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
> index 4033565393..595fdcdad8 100644
> --- a/target/riscv/insn32.decode
> +++ b/target/riscv/insn32.decode
> @@ -149,7 +149,12 @@ srl      0000000 .....    ..... 101 ..... 0110011 @r
>  sra      0100000 .....    ..... 101 ..... 0110011 @r
>  or       0000000 .....    ..... 110 ..... 0110011 @r
>  and      0000000 .....    ..... 111 ..... 0110011 @r
> -fence    ---- pred:4 succ:4 ----- 000 ----- 0001111
> +
> +{
> +  pause  0000 0001   0000   00000 000 00000 0001111
> +  fence  ---- pred:4 succ:4 ----- 000 ----- 0001111
> +}
> +
>  fence_i  ---- ----   ----   ----- 001 ----- 0001111
>  csrrw    ............     ..... 001 ..... 1110011 @csr
>  csrrs    ............     ..... 010 ..... 1110011 @csr
> diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
> index f1342f30f8..528c30c9a2 100644
> --- a/target/riscv/insn_trans/trans_rvi.c.inc
> +++ b/target/riscv/insn_trans/trans_rvi.c.inc
> @@ -18,6 +18,12 @@
>   * this program.  If not, see <http://www.gnu.org/licenses/>.
>   */
>  
> +#define REQUIRE_ZIHINTPAUSE(ctx) do { \
> +    if (!ctx->cfg_ptr->ext_zihintpause) {      \
> +        return false;         \
> +    }                         \
> +} while (0)
> +
>  static bool trans_illegal(DisasContext *ctx, arg_empty *a)
>  {
>      gen_exception_illegal(ctx);
> @@ -796,6 +802,18 @@ static bool trans_srad(DisasContext *ctx, arg_srad *a)
>      return gen_shift(ctx, a, EXT_SIGN, tcg_gen_sar_tl, NULL);
>  }
>  
> +static bool trans_pause(DisasContext *ctx, arg_pause *a)
> +{
> +    REQUIRE_ZIHINTPAUSE(ctx);
> +
> +    /*
> +     * PAUSE is a no-op in QEMU,
> +     * however we need to clear the reservation
> +     */
> +    tcg_gen_movi_tl(load_res, -1);
> +
> +    return true;
> +}
>  
>  static bool trans_fence(DisasContext *ctx, arg_fence *a)
>  {
>