Re: [Qemu-devel] [PATCH] Revert "memory: syncronize kvm bitmap using bitmaps operations"

[Paolo Bonzini <pbonzini@redhat.com>]

Il 29/01/2014 09:12, Alexey Kardashevskiy ha scritto:
> On 01/29/2014 06:30 PM, Paolo Bonzini wrote:
>> Il 29/01/2014 06:50, Alexey Kardashevskiy ha scritto:
>>> Since 64K system page size is quite popular configuration on PPC64,
>>> the original patch breaks migration.
>>>
>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>> ---
>>>  include/exec/ram_addr.h | 54
>>> +++++++++++++++++--------------------------------
>>>  1 file changed, 18 insertions(+), 36 deletions(-)
>>>
>>> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
>>> index 33c8acc..c6736ed 100644
>>> --- a/include/exec/ram_addr.h
>>> +++ b/include/exec/ram_addr.h
>>> @@ -83,47 +83,29 @@ static inline void
>>> cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
>>>                                                            ram_addr_t start,
>>>                                                            ram_addr_t pages)
>>>  {
>>> -    unsigned long i, j;
>>> +    unsigned int i, j;
>>>      unsigned long page_number, c;
>>>      hwaddr addr;
>>>      ram_addr_t ram_addr;
>>> -    unsigned long len = (pages + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
>>> +    unsigned int len = (pages + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
>>>      unsigned long hpratio = getpagesize() / TARGET_PAGE_SIZE;
>>> -    unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
>>>
>>> -    /* start address is aligned at the start of a word? */
>>> -    if (((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) {
>>
>> Why not just add " && hpratio == 1" here?
>
> Or fix dirty map to make it 1 bit per system page size (may be the fix is
> coming, who knows, but I am just not ready to do this now). Or do tricks
> with bits and support hpratio!=1. I could not choose and decided to revert
> it for now :)

Can you post the patch that adds " && hpratio == 1"?

> Do we really earn a lot here?

Yes, because this is the only part of migration that runs with the 
iothread lock taken.  Without Juan's patches you can see large guests 
hiccups that last a few seconds.

Paolo