Re: [PATCH 2/6] qemu-kvm: Modify and introduce wrapper functions to access phys_ram_dirty.

Yoshiaki Tamura
2010-03-16T22:51:10Z

Anthony Liguori wrote:
> On 03/16/2010 07:45 AM, Avi Kivity wrote:
>> On 03/16/2010 12:53 PM, Yoshiaki Tamura wrote:
>>> Modifies wrapper functions for byte-based phys_ram_dirty bitmap to
>>> bit-based phys_ram_dirty bitmap, and adds more wrapper functions to
>>> prevent
>>> direct access to the phys_ram_dirty bitmap.
>>
>>> +
>>> +static inline int cpu_physical_memory_get_dirty_flags(ram_addr_t addr)
>>> +{
>>> + unsigned long mask;
>>> + int index = (addr>> TARGET_PAGE_BITS) / HOST_LONG_BITS;
>>> + int offset = (addr>> TARGET_PAGE_BITS)& (HOST_LONG_BITS - 1);
>>> + int ret = 0;
>>> +
>>> + mask = 1UL<< offset;
>>> + if (phys_ram_vga_dirty[index]& mask)
>>> + ret |= VGA_DIRTY_FLAG;
>>> + if (phys_ram_code_dirty[index]& mask)
>>> + ret |= CODE_DIRTY_FLAG;
>>> + if (phys_ram_migration_dirty[index]& mask)
>>> + ret |= MIGRATION_DIRTY_FLAG;
>>> +
>>> + return ret;
>>> }
>>>
>>> static inline int cpu_physical_memory_get_dirty(ram_addr_t addr,
>>> int dirty_flags)
>>> {
>>> - return phys_ram_dirty[addr>> TARGET_PAGE_BITS]& dirty_flags;
>>> + return cpu_physical_memory_get_dirty_flags(addr)& dirty_flags;
>>> }
>>
>> This turns one cacheline access into three. If the dirty bitmaps were
>> in an array, you could do
>>
>> return dirty_bitmaps[dirty_index][addr >> (TARGET_PAGE_BITS +
>> BITS_IN_LONG)] & mask;
>>
>> with one cacheline access.
>
> As far as I can tell, we only ever call with a single flag so your
> suggestion makes sense.
>
> I'd suggest introducing these functions before splitting the bitmap up.
> It makes review a bit easier.

Thanks for your advise.
I'll post the wrapper functions for existing byte-based phys_ram_dirty first.

Yoshi