Compute the value using straight division and bounds,
rather than a loop.  Pass in tb_size rather than reading
from tcg_init_ctx.code_gen_buffer_size,

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/region.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/tcg/region.c b/tcg/region.c
index bd81b35359..b44246e1aa 100644
--- a/tcg/region.c
+++ b/tcg/region.c
@@ -363,38 +363,33 @@ void tcg_region_reset_all(void)
     tcg_region_tree_reset_all();
 }
 
-static size_t tcg_n_regions(unsigned max_cpus)
+static size_t tcg_n_regions(size_t tb_size, unsigned max_cpus)
 {
 #ifdef CONFIG_USER_ONLY
     return 1;
 #else
+    size_t n_regions;
+
     /*
      * It is likely that some vCPUs will translate more code than others,
      * so we first try to set more regions than max_cpus, with those regions
      * being of reasonable size. If that's not possible we make do by evenly
      * dividing the code_gen_buffer among the vCPUs.
      */
-    size_t i;
-
     /* Use a single region if all we have is one vCPU thread */
     if (max_cpus == 1 || !qemu_tcg_mttcg_enabled()) {
         return 1;
     }
 
-    /* Try to have more regions than max_cpus, with each region being >= 2 MB */
-    for (i = 8; i > 0; i--) {
-        size_t regions_per_thread = i;
-        size_t region_size;
-
-        region_size = tcg_init_ctx.code_gen_buffer_size;
-        region_size /= max_cpus * regions_per_thread;
-
-        if (region_size >= 2 * 1024u * 1024) {
-            return max_cpus * regions_per_thread;
-        }
+    /*
+     * Try to have more regions than max_cpus, with each region being >= 2 MB.
+     * If we can't, then just allocate one region per vCPU thread.
+     */
+    n_regions = tb_size / (2 * MiB);
+    if (n_regions <= max_cpus) {
+        return max_cpus;
     }
-    /* If we can't, then just allocate one region per vCPU thread */
-    return max_cpus;
+    return MIN(n_regions, max_cpus * 8);
 #endif
 }
 
@@ -828,7 +823,7 @@ void tcg_region_init(size_t tb_size, int splitwx, unsigned max_cpus)
     buf = tcg_init_ctx.code_gen_buffer;
     total_size = tcg_init_ctx.code_gen_buffer_size;
     page_size = qemu_real_host_page_size;
-    n_regions = tcg_n_regions(max_cpus);
+    n_regions = tcg_n_regions(total_size, max_cpus);
 
     /* The first region will be 'aligned - buf' bytes larger than the others */
     aligned = QEMU_ALIGN_PTR_UP(buf, page_size);
-- 
2.25.1

Richard Henderson <richard.henderson@linaro.org> writes:

> Compute the value using straight division and bounds,
> rather than a loop.  Pass in tb_size rather than reading
> from tcg_init_ctx.code_gen_buffer_size,
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/region.c | 29 ++++++++++++-----------------
>  1 file changed, 12 insertions(+), 17 deletions(-)
>
> diff --git a/tcg/region.c b/tcg/region.c
> index bd81b35359..b44246e1aa 100644
> --- a/tcg/region.c
> +++ b/tcg/region.c
> @@ -363,38 +363,33 @@ void tcg_region_reset_all(void)
>      tcg_region_tree_reset_all();
>  }
>  
> -static size_t tcg_n_regions(unsigned max_cpus)
> +static size_t tcg_n_regions(size_t tb_size, unsigned max_cpus)
>  {
>  #ifdef CONFIG_USER_ONLY
>      return 1;
>  #else
> +    size_t n_regions;
> +
>      /*
>       * It is likely that some vCPUs will translate more code than others,
>       * so we first try to set more regions than max_cpus, with those regions
>       * being of reasonable size. If that's not possible we make do by evenly
>       * dividing the code_gen_buffer among the vCPUs.
>       */
> -    size_t i;
> -
>      /* Use a single region if all we have is one vCPU thread */
>      if (max_cpus == 1 || !qemu_tcg_mttcg_enabled()) {
>          return 1;
>      }
>  
> -    /* Try to have more regions than max_cpus, with each region being >= 2 MB */
> -    for (i = 8; i > 0; i--) {
> -        size_t regions_per_thread = i;
> -        size_t region_size;
> -
> -        region_size = tcg_init_ctx.code_gen_buffer_size;
> -        region_size /= max_cpus * regions_per_thread;
> -
> -        if (region_size >= 2 * 1024u * 1024) {
> -            return max_cpus * regions_per_thread;
> -        }
> +    /*
> +     * Try to have more regions than max_cpus, with each region being >= 2 MB.
> +     * If we can't, then just allocate one region per vCPU thread.
> +     */
> +    n_regions = tb_size / (2 * MiB);
> +    if (n_regions <= max_cpus) {
> +        return max_cpus;
>      }
> -    /* If we can't, then just allocate one region per vCPU thread */
> -    return max_cpus;
> +    return MIN(n_regions, max_cpus * 8);
>  #endif
>  }

This is so much easier to follow now ;-)

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée

From: Richard Henderson <richard.henderson@linaro.org>
> Compute the value using straight division and bounds, rather than a loop.  Pass
> in tb_size rather than reading from tcg_init_ctx.code_gen_buffer_size,
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/region.c | 29 ++++++++++++-----------------
>  1 file changed, 12 insertions(+), 17 deletions(-)

Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>

--
Luis Pires
Instituto de Pesquisas ELDORADO
Aviso Legal - Disclaimer <https://www.eldorado.org.br/disclaimer.html>