[Qemu-devel] Re: [PATCH] qemu-kvm: Speed up of the dirty-bitmap-traveling

[Avi Kivity]

On 02/10/2010 11:55 AM, OHMURA Kei wrote:
>
>> Instead of using a nested loop if bitmap_ul[i] != 0, it is possible to
>> use just a single loop (while (c>  0)), and process a long's worth of data.
>>
>> The only trickery is with big endian hosts, where the conversion from
>> bit number to page number is a bit complicated.
>>     
> To convert the bitmap from big endian to little endian, le_bswap macro in
> bswap.h seems useful, which is now undefined.  What do you think about this
> approach?
>
> This is an example bitmap-traveling code using le_bswap:
>      /* 
>       * bitmap-traveling is faster than memory-traveling (for addr...) 
>       * especially when most of the memory is not dirty.
>       */
>      for (i = 0; i < len; i++) {
>         if (bitmap_ul[i] != 0) {
>             c = le_bswap(bitmap_ul[i], HOST_LONG_BITS);
>             while (c > 0) {
>                 j = ffsl(c) - 1;
>                 c &= ~(1ul << j);
>                 page_number = i * HOST_LONG_BITS + j;
>                 addr1 = page_number * TARGET_PAGE_SIZE;
>                 addr = offset + addr1;
>                 ram_addr = cpu_get_physical_page_desc(addr);
>                 cpu_physical_memory_set_dirty(ram_addr);
>             }
>          }
>      }
>   

Yes, that solves the problem very neatly.

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