Re: [Qemu-devel] [patch v5 6/8] memory: make mmio dispatch able to be out of biglock

[Avi Kivity <avi@redhat.com>]

On 10/29/2012 01:48 AM, Liu Ping Fan wrote:
> Without biglock, we try to protect the mr by increase refcnt.
> If we can inc refcnt, go backward and resort to biglock.
> 
> Another point is memory radix-tree can be flushed by another
> thread, so we should get the copy of terminal mr to survive
> from such issue.
> 

> +static bool memory_region_section_ref(MemoryRegionSection *mrs)
> +{
> +    MemoryRegion *mr;
> +    bool ret = false;
> +
> +    mr = mrs->mr;
> +    if (mr->ops && mr->ops->ref) {
> +        ret = mr->ops->ref(mr);

I still don't see why ->ref() needs to return something.

> +    }
> +    return ret;
> +}
> +
>  
>      while (len > 0) {
>          page = addr & TARGET_PAGE_MASK;
>          l = (page + TARGET_PAGE_SIZE) - addr;
>          if (l > len)
>              l = len;
> -        section = phys_page_find(d, page >> TARGET_PAGE_BITS);
> +
> +        if (as->lock) {
> +            qemu_mutex_lock(as->lock);
> +            safe_ref = memory_region_section_lookup_ref(d, page, &obj_mrs);
> +            qemu_mutex_unlock(as->lock);
> +            if (!safe_ref) {
> +                qemu_mutex_lock_iothread();
> +                qemu_mutex_lock(as->lock);
> +                /* when 2nd try, mem map can change, need to judge it again */
> +                safe_ref = memory_region_section_lookup_ref(d, page, &obj_mrs);
> +                qemu_mutex_unlock(as->lock);
> +                if (safe_ref) {
> +                    qemu_mutex_unlock_iothread();
> +                }
> +            }
> +        } else {
> +            /* Caller hold the big lock */
> +            memory_region_section_lookup_ref(d, page, &obj_mrs);

It's not a property of the address space, it's a property of the caller.

> +        }
> +        section = &obj_mrs;
>  
>          if (is_write) {
>              if (!memory_region_is_ram(section->mr)) {


-- 
error compiling committee.c: too many arguments to function