Re: [Qemu-devel] [RFC PATCH V7 13/19] add a callback when tb_invalidate is called.

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/08/2015 17:27, fred.konrad@greensocs.com wrote:
> From: KONRAD Frederic <fred.konrad@greensocs.com>
> 
> Instead of doing the jump cache invalidation directly in tb_invalidate delay it
> after the exit so we don't have an other CPU trying to execute the code being
> invalidated.
> 
> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> ---
>  translate-all.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 59 insertions(+), 2 deletions(-)

If you take the easy way and avoid the optimizations in patch 7, this is
not necessary: tb_find_fast and tb_add_jump are only called from within
tb_lock, so all of tb_jmp_cache/jmp_first/jmp_next are protected by tb_lock.

Let's get everything in and then optimize; the order should be:

- Alvise's LL/SC implementation

- conversion of atomics to LL/SC for all front-ends

- the main MTTCG series, reusing the locking already in-place for
user-mode emulation (with some audit...)

- any further push-downs of tb_lock

Paolo

> diff --git a/translate-all.c b/translate-all.c
> index 954c67a..fc5162a 100644
> --- a/translate-all.c
> +++ b/translate-all.c
> @@ -62,6 +62,7 @@
>  #include "translate-all.h"
>  #include "qemu/bitmap.h"
>  #include "qemu/timer.h"
> +#include "sysemu/cpus.h"
>  
>  //#define DEBUG_TB_INVALIDATE
>  //#define DEBUG_FLUSH
> @@ -967,14 +968,58 @@ static inline void tb_reset_jump(TranslationBlock *tb, int n)
>      tb_set_jmp_target(tb, n, (uintptr_t)(tb->tc_ptr + tb->tb_next_offset[n]));
>  }
>  
> +struct CPUDiscardTBParams {
> +    CPUState *cpu;
> +    TranslationBlock *tb;
> +};
> +
> +static void cpu_discard_tb_from_jmp_cache(void *opaque)
> +{
> +    unsigned int h;
> +    struct CPUDiscardTBParams *params = opaque;
> +
> +    h = tb_jmp_cache_hash_func(params->tb->pc);
> +    if (params->cpu->tb_jmp_cache[h] == params->tb) {
> +        params->cpu->tb_jmp_cache[h] = NULL;
> +    }
> +
> +    g_free(opaque);
> +}
> +
> +static void tb_invalidate_jmp_remove(void *opaque)
> +{
> +    TranslationBlock *tb = opaque;
> +    TranslationBlock *tb1, *tb2;
> +    unsigned int n1;
> +
> +    /* suppress this TB from the two jump lists */
> +    tb_jmp_remove(tb, 0);
> +    tb_jmp_remove(tb, 1);
> +
> +    /* suppress any remaining jumps to this TB */
> +    tb1 = tb->jmp_first;
> +    for (;;) {
> +        n1 = (uintptr_t)tb1 & 3;
> +        if (n1 == 2) {
> +            break;
> +        }
> +        tb1 = (TranslationBlock *)((uintptr_t)tb1 & ~3);
> +        tb2 = tb1->jmp_next[n1];
> +        tb_reset_jump(tb1, n1);
> +        tb1->jmp_next[n1] = NULL;
> +        tb1 = tb2;
> +    }
> +    tb->jmp_first = (TranslationBlock *)((uintptr_t)tb | 2); /* fail safe */
> +}
> +
>  /* invalidate one TB */
>  void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>  {
>      CPUState *cpu;
>      PageDesc *p;
> -    unsigned int h, n1;
> +    unsigned int h;
>      tb_page_addr_t phys_pc;
> -    TranslationBlock *tb1, *tb2;
> +    struct CPUDiscardTBParams *params;
>  
>      tb_lock();
>  
> @@ -997,6 +1042,9 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>  
>      tcg_ctx.tb_ctx.tb_invalidated_flag = 1;
>  
> +#if 0 /*MTTCG*/
> +    TranslationBlock *tb1, *tb2;
> +    unsigned int n1;
>      /* remove the TB from the hash list */
>      h = tb_jmp_cache_hash_func(tb->pc);
>      CPU_FOREACH(cpu) {
> @@ -1023,6 +1071,15 @@ void tb_phys_invalidate(TranslationBlock *tb, tb_page_addr_t page_addr)
>          tb1 = tb2;
>      }
>      tb->jmp_first = (TranslationBlock *)((uintptr_t)tb | 2); /* fail safe */
> +#else
> +    CPU_FOREACH(cpu) {
> +        params = g_malloc(sizeof(struct CPUDiscardTBParams));
> +        params->cpu = cpu;
> +        params->tb = tb;
> +        async_run_on_cpu(cpu, cpu_discard_tb_from_jmp_cache, params);
> +    }
> +    async_run_safe_work_on_cpu(first_cpu, tb_invalidate_jmp_remove, tb);
> +#endif /* MTTCG */
>  
>      tcg_ctx.tb_ctx.tb_phys_invalidate_count++;
>      tb_unlock();
>