Re: [Qemu-devel] [PATCHv2 1/3] qemu: memory notifiers

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 18, 2010 at 03:58:51PM +0200, Avi Kivity wrote:
> On 01/18/2010 03:52 PM, Michael S. Tsirkin wrote:
>> On Mon, Jan 18, 2010 at 03:02:59PM +0200, Avi Kivity wrote:
>>    
>>> On 01/04/2010 09:49 PM, Michael S. Tsirkin wrote:
>>>      
>>>> This adds notifiers for phys memory changes: a set of callbacks that
>>>> vhost can register and update kernel accordingly.  Down the road, kvm
>>>> code can be switched to use these as well, instead of calling kvm code
>>>> directly from exec.c as is done now.
>>>>
>>>>
>>>> +
>>>> +static void phys_page_for_each_in_l1_map(PhysPageDesc **phys_map,
>>>> +                                         CPUPhysMemoryClient *client)
>>>> +{
>>>> +    PhysPageDesc *pd;
>>>> +    int l1, l2;
>>>> +
>>>> +    for (l1 = 0; l1<   L1_SIZE; ++l1) {
>>>> +        pd = phys_map[l1];
>>>> +        if (!pd) {
>>>> +            continue;
>>>> +        }
>>>> +        for (l2 = 0; l2<   L2_SIZE; ++l2) {
>>>> +            if (pd[l2].phys_offset == IO_MEM_UNASSIGNED) {
>>>> +                continue;
>>>> +            }
>>>> +            client->set_memory(client, pd[l2].region_offset,
>>>> +                               TARGET_PAGE_SIZE, pd[l2].phys_offset);
>>>> +        }
>>>> +    }
>>>> +}
>>>> +
>>>> +static void phys_page_for_each(CPUPhysMemoryClient *client)
>>>> +{
>>>> +#if TARGET_PHYS_ADDR_SPACE_BITS>   32
>>>> +
>>>> +#if TARGET_PHYS_ADDR_SPACE_BITS>   (32 + L1_BITS)
>>>> +#error unsupported TARGET_PHYS_ADDR_SPACE_BITS
>>>> +#endif
>>>> +    void **phys_map = (void **)l1_phys_map;
>>>> +    int l1;
>>>> +    if (!l1_phys_map) {
>>>> +        return;
>>>> +    }
>>>> +    for (l1 = 0; l1<   L1_SIZE; ++l1) {
>>>> +        if (phys_map[l1]) {
>>>> +            phys_page_for_each_in_l1_map(phys_map[l1], client);
>>>> +        }
>>>> +    }
>>>> +#else
>>>> +    if (!l1_phys_map) {
>>>> +        return;
>>>> +    }
>>>> +    phys_page_for_each_in_l1_map(l1_phys_map, client);
>>>> +#endif
>>>> +}
>>>>
>>>>        
>>> This looks pretty frightening.  What is it needed for?
>>>      
>> The point is that clients can be registered at any point.
>>
>> A client that registered when memory is present needs to
>> be notified about it.
>>    
>
> It looks very expensive.

Shouldn't be hard to optimize ...

> Maybe we mandate clients be registered at init-time?


This might be tricky - vhost currently only registers when the
first device is hot-added.

> Long term we need to move to a range based memory description.
>
> -- 
> error compiling committee.c: too many arguments to function