Re: [Qemu-devel] [RFC 35/38] cputlb: use cpu_tcg_sched_work for tlb_flush_all

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/08/2015 17:24, Emilio G. Cota wrote:
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---
>  cputlb.c | 41 +++++++++++------------------------------
>  1 file changed, 11 insertions(+), 30 deletions(-)

As suggested by me and Peter, synchronization on TLB flushes should be
arch-specific.  CPUs can halt on a dmb if they have pending TLB flush
requests on other CPUs, and the CPU can be woken up from the run_on_cpu
callback with something like:

    if (--caller_cpu->pending_tlb_flush_request) {
        caller_cpu->interrupt_request |= CPU_INTERRUPT_TLB_DONE;
        qemu_cpu_kick(caller_cpu);
    }


...


static bool arm_cpu_has_work(CPUState *cs)
{
    ARMCPU *cpu = ARM_CPU(cs);

    return !cpu->pending_tlb_flush_request && !cpu->powered_off
        && cs->interrupt_request &
        (CPU_INTERRUPT_FIQ | CPU_INTERRUPT_HARD
         | CPU_INTERRUPT_VFIQ | CPU_INTERRUPT_VIRQ
         | CPU_INTERRUPT_EXITTB | CPU_INTERRUPT_TLB_DONE);
}

Paolo

> diff --git a/cputlb.c b/cputlb.c
> index 1b3673e..d81a4eb 100644
> --- a/cputlb.c
> +++ b/cputlb.c
> @@ -73,43 +73,24 @@ void tlb_flush(CPUState *cpu, int flush_global)
>      tlb_flush_count++;
>  }
>  
> -struct TLBFlushParams {
> -    CPUState *cpu;
> -    int flush_global;
> -};
> -
> -static void tlb_flush_async_work(void *opaque)
> +static void __tlb_flush_all(void *arg)
>  {
> -    struct TLBFlushParams *params = opaque;
> +    CPUState *cpu;
> +    int flush_global = *(int *)arg;
>  
> -    tlb_flush(params->cpu, params->flush_global);
> -    g_free(params);
> +    CPU_FOREACH(cpu) {
> +        tlb_flush(cpu, flush_global);
> +    }
> +    g_free(arg);
>  }
>  
>  void tlb_flush_all(int flush_global)
>  {
> -    CPUState *cpu;
> -    struct TLBFlushParams *params;
> +    int *arg = g_malloc(sizeof(*arg));
>  
> -#if 0 /* MTTCG */
> -    CPU_FOREACH(cpu) {
> -        tlb_flush(cpu, flush_global);
> -    }
> -#else
> -    CPU_FOREACH(cpu) {
> -        if (qemu_cpu_is_self(cpu)) {
> -            /* async_run_on_cpu handle this case but this just avoid a malloc
> -             * here.
> -             */
> -            tlb_flush(cpu, flush_global);
> -        } else {
> -            params = g_malloc(sizeof(struct TLBFlushParams));
> -            params->cpu = cpu;
> -            params->flush_global = flush_global;
> -            async_run_on_cpu(cpu, tlb_flush_async_work, params);
> -        }
> -    }
> -#endif /* MTTCG */
> +    *arg = flush_global;
> +    tb_lock();
> +    cpu_tcg_sched_work(current_cpu, __tlb_flush_all, arg);
>  }
>  
>  static inline void tlb_flush_entry(CPUTLBEntry *tlb_entry, target_ulong addr)
>