Re: [Qemu-devel] [PATCH v2] translate-all: use bitmap helpers for PageDesc's bitmap

[Paolo Bonzini <pbonzini@redhat.com>]

On 22/04/2015 18:53, Emilio G. Cota wrote:
> Here we have an open-coded byte-based bitmap implementation.
> Get rid of it since there's a ulong-based implementation to be
> used by all code.
> 
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---
>  translate-all.c | 40 +++++++---------------------------------
>  1 file changed, 7 insertions(+), 33 deletions(-)
> 
> diff --git a/translate-all.c b/translate-all.c
> index acf792c..9592a3b 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -59,6 +59,7 @@
>  
>  #include "exec/cputlb.h"
>  #include "translate-all.h"
> +#include "qemu/bitmap.h"
>  #include "qemu/timer.h"
>  
>  //#define DEBUG_TB_INVALIDATE
> @@ -79,7 +80,7 @@ typedef struct PageDesc {
>      /* in order to optimize self modifying code, we count the number
>         of lookups we do to a given page to use a bitmap */
>      unsigned int code_write_count;
> -    uint8_t *code_bitmap;
> +    unsigned long *code_bitmap;
>  #if defined(CONFIG_USER_ONLY)
>      unsigned long flags;
>  #endif
> @@ -964,39 +965,12 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>      tcg_ctx.tb_ctx.tb_phys_invalidate_count++;
>  }
>  
> -static inline void set_bits(uint8_t *tab, int start, int len)
> -{
> -    int end, mask, end1;
> -
> -    end = start + len;
> -    tab += start >> 3;
> -    mask = 0xff << (start & 7);
> -    if ((start & ~7) == (end & ~7)) {
> -        if (start < end) {
> -            mask &= ~(0xff << (end & 7));
> -            *tab |= mask;
> -        }
> -    } else {
> -        *tab++ |= mask;
> -        start = (start + 8) & ~7;
> -        end1 = end & ~7;
> -        while (start < end1) {
> -            *tab++ = 0xff;
> -            start += 8;
> -        }
> -        if (start < end) {
> -            mask = ~(0xff << (end & 7));
> -            *tab |= mask;
> -        }
> -    }
> -}
> -
>  static void build_page_bitmap(PageDesc *p)
>  {
>      int n, tb_start, tb_end;
>      TranslationBlock *tb;
>  
> -    p->code_bitmap = g_malloc0(TARGET_PAGE_SIZE / 8);
> +    p->code_bitmap = bitmap_new(TARGET_PAGE_SIZE);
>  
>      tb = p->first_tb;
>      while (tb != NULL) {
> @@ -1015,7 +989,7 @@ static void build_page_bitmap(PageDesc *p)
>              tb_start = 0;
>              tb_end = ((tb->pc + tb->size) & ~TARGET_PAGE_MASK);
>          }
> -        set_bits(p->code_bitmap, tb_start, tb_end - tb_start);
> +        bitmap_set(p->code_bitmap, tb_start, tb_end - tb_start);
>          tb = tb->page_next[n];
>      }
>  }
> @@ -1205,7 +1179,6 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
>  void tb_invalidate_phys_page_fast(tb_page_addr_t start, int len)
>  {
>      PageDesc *p;
> -    int offset, b;
>  
>  #if 0
>      if (1) {
> @@ -1221,8 +1194,9 @@ void tb_invalidate_phys_page_fast(tb_page_addr_t start, int len)
>          return;
>      }
>      if (p->code_bitmap) {
> -        offset = start & ~TARGET_PAGE_MASK;
> -        b = p->code_bitmap[offset >> 3] >> (offset & 7);
> +        int nr = start & ~TARGET_PAGE_MASK;

This should be unsigned, otherwise the compiler might not make
BIT_WORD(nr) a simple right shift (maybe it can see that nr > 0 thanks
to the AND, but in principle x / 32 is not the same as x >> 5 if x is
signed).

> +        int b = p->code_bitmap[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG - 1));

And this should be unsigned long.

Otherwise looks good.

Paolo

> +
>          if (b & ((1 << len) - 1)) {
>              goto do_invalidate;
>          }
>