Re: [Qemu-devel] [RFC v6 09/14] softmmu: Add history of excl accesses

[Paolo Bonzini]

On 14/12/2015 09:41, Alvise Rigo wrote:
> +static inline void excl_history_put_addr(CPUState *cpu, hwaddr addr)
> +{
> +    /* Avoid some overhead if the address we are about to put is equal to
> +     * the last one */
> +    if (cpu->excl_protected_addr[cpu->excl_protected_last] !=
> +                                    (addr & TARGET_PAGE_MASK)) {
> +        cpu->excl_protected_last = (cpu->excl_protected_last + 1) %
> +                                            EXCLUSIVE_HISTORY_LEN;

Either use "&" here...

> +        /* Unset EXCL bit of the oldest entry */
> +        if (cpu->excl_protected_addr[cpu->excl_protected_last] !=
> +                                            EXCLUSIVE_RESET_ADDR) {
> +            cpu_physical_memory_unset_excl(
> +                cpu->excl_protected_addr[cpu->excl_protected_last],
> +                cpu->cpu_index);
> +        }
> +
> +        /* Add a new address, overwriting the oldest one */
> +        cpu->excl_protected_addr[cpu->excl_protected_last] =
> +                                            addr & TARGET_PAGE_MASK;
> +    }
> +}
> +
>  #define MMUSUFFIX _mmu
>  
>  /* Generates LoadLink/StoreConditional helpers in softmmu_template.h */
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 9e409ce..5f65ebf 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -217,6 +217,7 @@ struct kvm_run;
>  
>  /* Atomic insn translation TLB support. */
>  #define EXCLUSIVE_RESET_ADDR ULLONG_MAX
> +#define EXCLUSIVE_HISTORY_LEN 8
>  
>  /**
>   * CPUState:
> @@ -343,6 +344,8 @@ struct CPUState {
>       * The address is set to EXCLUSIVE_RESET_ADDR if the vCPU is not.
>       * in the middle of a LL/SC. */
>      struct Range excl_protected_range;
> +    hwaddr excl_protected_addr[EXCLUSIVE_HISTORY_LEN];
> +    int excl_protected_last;

... or make this an "unsigned int".  Otherwise the code will contain an
actual (and slow) modulo operation.

Paolo

>      /* Used to carry the SC result but also to flag a normal (legacy)
>       * store access made by a stcond (see softmmu_template.h). */
>      int excl_succeeded;