Re: [Qemu-devel] [RFC 02/10] use a different translation block list for each cpu.

["Alex Bennée" <alex.bennee@linaro.org>]

fred.konrad@greensocs.com writes:

> From: KONRAD Frederic <fred.konrad@greensocs.com>
>
> We need a different TranslationBlock list for each core in case of multithread
> TCG.
>
> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> ---
>  translate-all.c | 40 ++++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 18 deletions(-)
>
> diff --git a/translate-all.c b/translate-all.c
> index 8fa4378..0e11c70 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -72,10 +72,11 @@
>  #endif
>  
>  #define SMC_BITMAP_USE_THRESHOLD 10
> +#define MAX_CPUS 256

Where does this number come from?

>  typedef struct PageDesc {
>      /* list of TBs intersecting this ram page */
> -    TranslationBlock *first_tb;
> +    TranslationBlock *first_tb[MAX_CPUS];

Especially given the size of the PageDesc structure this adds a lot of
of bulk, mostly unused. Is the access to the TB list via PageDesc that
frequent to avoid an additional indirection?

>      /* 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;
> @@ -750,7 +751,7 @@ static inline void invalidate_page_bitmap(PageDesc *p)
>  /* Set to NULL all the 'first_tb' fields in all PageDescs. */
>  static void page_flush_tb_1(int level, void **lp)
>  {
> -    int i;
> +    int i, j;
>  
>      if (*lp == NULL) {
>          return;
> @@ -759,7 +760,9 @@ static void page_flush_tb_1(int level, void **lp)
>          PageDesc *pd = *lp;
>  
>          for (i = 0; i < V_L2_SIZE; ++i) {
> -            pd[i].first_tb = NULL;
> +            for (j = 0; j < MAX_CPUS; j++) {
> +                pd[i].first_tb[j] = NULL;
> +            }
>              invalidate_page_bitmap(pd + i);
>          }
>      } else {
> @@ -937,12 +940,12 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>      /* remove the TB from the page list */
>      if (tb->page_addr[0] != page_addr) {
>          p = page_find(tb->page_addr[0] >> TARGET_PAGE_BITS);
> -        tb_page_remove(&p->first_tb, tb);
> +        tb_page_remove(&p->first_tb[current_cpu->cpu_index], tb);
>          invalidate_page_bitmap(p);
>      }
>      if (tb->page_addr[1] != -1 && tb->page_addr[1] != page_addr) {
>          p = page_find(tb->page_addr[1] >> TARGET_PAGE_BITS);
> -        tb_page_remove(&p->first_tb, tb);
> +        tb_page_remove(&p->first_tb[current_cpu->cpu_index], tb);
>          invalidate_page_bitmap(p);
>      }
>  
> @@ -1012,7 +1015,7 @@ static void build_page_bitmap(PageDesc *p)
>  
>      p->code_bitmap = g_malloc0(TARGET_PAGE_SIZE / 8);
>  
> -    tb = p->first_tb;
> +    tb = p->first_tb[current_cpu->cpu_index];
>      while (tb != NULL) {
>          n = (uintptr_t)tb & 3;
>          tb = (TranslationBlock *)((uintptr_t)tb & ~3);
> @@ -1138,7 +1141,7 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
>      /* we remove all the TBs in the range [start, end[ */
>      /* XXX: see if in some cases it could be faster to invalidate all
>         the code */
> -    tb = p->first_tb;
> +    tb = p->first_tb[cpu->cpu_index];
>      while (tb != NULL) {
>          n = (uintptr_t)tb & 3;
>          tb = (TranslationBlock *)((uintptr_t)tb & ~3);
> @@ -1196,7 +1199,7 @@ void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
>      }
>  #if !defined(CONFIG_USER_ONLY)
>      /* if no code remaining, no need to continue to use slow writes */
> -    if (!p->first_tb) {
> +    if (!p->first_tb[cpu->cpu_index]) {
>          invalidate_page_bitmap(p);
>          if (is_cpu_write_access) {
>              tlb_unprotect_code_phys(cpu, start, cpu->mem_io_vaddr);
> @@ -1224,10 +1227,10 @@ void tb_invalidate_phys_page_fast(tb_page_addr_t start, int len)
>  #if 0
>      if (1) {
>          qemu_log("modifying code at 0x%x size=%d EIP=%x PC=%08x\n",
> -                  cpu_single_env->mem_io_vaddr, len,
> -                  cpu_single_env->eip,
> -                  cpu_single_env->eip +
> -                  (intptr_t)cpu_single_env->segs[R_CS].base);
> +                  current_cpu->mem_io_vaddr, len,
> +                  current_cpu->eip,
> +                  current_cpu->eip +
> +                  (intptr_t)current_cpu->segs[R_CS].base);
>      }
>  #endif
>      p = page_find(start >> TARGET_PAGE_BITS);
> @@ -1269,7 +1272,7 @@ static void tb_invalidate_phys_page(tb_page_addr_t addr,
>      if (!p) {
>          return;
>      }
> -    tb = p->first_tb;
> +    tb = p->first_tb[current_cpu->cpu_index];
>  #ifdef TARGET_HAS_PRECISE_SMC
>      if (tb && pc != 0) {
>          current_tb = tb_find_pc(pc);
> @@ -1299,7 +1302,7 @@ static void tb_invalidate_phys_page(tb_page_addr_t addr,
>          tb_phys_invalidate(tb, addr);
>          tb = tb->page_next[n];
>      }
> -    p->first_tb = NULL;
> +    p->first_tb[current_cpu->cpu_index] = NULL;
>  #ifdef TARGET_HAS_PRECISE_SMC
>      if (current_tb_modified) {
>          /* we generate a block containing just the instruction
> @@ -1327,11 +1330,12 @@ static inline void tb_alloc_page(TranslationBlock *tb,
>  
>      tb->page_addr[n] = page_addr;
>      p = page_find_alloc(page_addr >> TARGET_PAGE_BITS, 1);
> -    tb->page_next[n] = p->first_tb;
> +    tb->page_next[n] = p->first_tb[current_cpu->cpu_index];
>  #ifndef CONFIG_USER_ONLY
> -    page_already_protected = p->first_tb != NULL;
> +    page_already_protected = p->first_tb[current_cpu->cpu_index] != NULL;
>  #endif
> -    p->first_tb = (TranslationBlock *)((uintptr_t)tb | n);
> +    p->first_tb[current_cpu->cpu_index]
> +      = (TranslationBlock *)((uintptr_t)tb | n);
>      invalidate_page_bitmap(p);
>  
>  #if defined(TARGET_HAS_SMC) || 1
> @@ -1821,7 +1825,7 @@ void page_set_flags(target_ulong start, target_ulong end, int flags)
>             the code inside.  */
>          if (!(p->flags & PAGE_WRITE) &&
>              (flags & PAGE_WRITE) &&
> -            p->first_tb) {
> +            p->first_tb[current_cpu->cpu_index]) {
>              tb_invalidate_phys_page(addr, 0, NULL, false);
>          }
>          p->flags = flags;

As the TranslationBlock itself has a linked list for page related
blocks:

  struct TranslationBlock *page_next[2];

could we not just come up with a structure that chains them together
here? 

-- 
Alex Bennée