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

[Peter Maydell]

On 16 January 2015 at 17:19,  <address@hidden> wrote:
> From: KONRAD Frederic <address@hidden>
>
> We need a different TranslationBlock list for each core in case of multithread
> TCG.
>
> Signed-off-by: KONRAD Frederic <address@hidden>
> ---
>  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
>
>  typedef struct PageDesc {
>      /* list of TBs intersecting this ram page */
> -    TranslationBlock *first_tb;
> +    TranslationBlock *first_tb[MAX_CPUS];

Do we really need to know this for every CPU, or just for
the one that's using this PageDesc? I am assuming we're going to make
the l1_map be per-CPU.

>      /* 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);

Anything using current_cpu in this code is hugely suspect.
For instance cpu_restore_state() takes a CPUState pointer and
calls this function -- either it should be acting on just that
CPU (which might not be the current one) or on all CPUs. In
any case implicitly working on current_cpu here is wrong.

Probably we need to look at the public-facing functions here
and decide which should have "operate on all CPUs" semantics
and which should have "operate on the CPU passed as a parameter"
and which "operate on the implicit current CPU".

-- PMM