[Qemu-devel] New Bitmap module ?

[Qemu-devel] New Bitmap module ?

[Corentin Chary]

Hi,
I was working on merging VNC updates into bigger ones to see if it
lower the overhead (big updates sometime use less network/cpu than a
lot of small updates).
For that, I needed some new bitmap functions, and no we got, in vnc.c:
- set_bit
- clear_bit
- set_bits
- clear_bits
- find_next_bit
- find_next_zero_bit
- find_next_zero_area

Should we move that into bitmap.c/bitmap.h ? Which part of QEMU could
use that (block.c maybe ?)
Thanks
-- 
Corentin Chary
http://xf.iksaif.net

Re: [Qemu-devel] New Bitmap module ?

[Andre Przywara]

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Corentin Chary wrote:
> Hi,
> I was working on merging VNC updates into bigger ones to see if it
> lower the overhead (big updates sometime use less network/cpu than a
> lot of small updates).
> For that, I needed some new bitmap functions, and no we got, in vnc.c:
> - set_bit
> - clear_bit
> - set_bits
> - clear_bits
> - find_next_bit
> - find_next_zero_bit
> - find_next_zero_area
> 
> Should we move that into bitmap.c/bitmap.h ?
Definitely! For my NUMA work I have also coded some bitmap functions.
Since mine are not performance critical, I reverted from implementing 
set_bits and clear_bits and replaced them with a loop in the calling 
code. So I could just could come around with a macro only 
implementation, for which a header file suffices (attached for reference).

> Which part of QEMU could
> use that (block.c maybe ?)
As mentioned, the yet to be submitted NUMA code would benefit from it. 
Linux has also bitmap code, maybe you could leverage this (if not 
already done).

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12

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#ifndef __BITMAP_H__
#define __BITMAP_H__

#ifndef HOST_LONG_BITS
#define HOST_LONG_BITS (sizeof(long) * 8)
#endif

#define bitmap_isset(bm,bit) \
    (!!bm[(bit) / HOST_LONG_BITS] & (1ULL << ((bit) % HOST_LONG_BITS)))
#define bitmap_set(bm,bit) \
    (bm[(bit) / HOST_LONG_BITS] |= (1ULL << ((bit) % HOST_LONG_BITS)))
#define bitmap_unset(bm,bit) \
    (bm[(bit) / HOST_LONG_BITS] &= ~(1ULL << ((bit) % HOST_LONG_BITS)))
#define DECLARE_BITMAP(bm,len) \
    unsigned long bm[((len) + HOST_LONG_BITS - 1) / HOST_LONG_BITS]
#define bitmap_clear(bm,len) \
    memset(bm, 0, (len + 7) / 8)
#define bitmap_fill(bm,len) \
    memset(bm, 0xFF, (len + 7) / 8)

#endif

Re: [Qemu-devel] New Bitmap module ?

[Corentin Chary]

On Thu, Jul 22, 2010 at 3:46 PM, Andre Przywara <andre.przywara@amd.com> wrote:
> Corentin Chary wrote:
>>
>> Hi,
>> I was working on merging VNC updates into bigger ones to see if it
>> lower the overhead (big updates sometime use less network/cpu than a
>> lot of small updates).
>> For that, I needed some new bitmap functions, and no we got, in vnc.c:
>> - set_bit
>> - clear_bit
>> - set_bits
>> - clear_bits
>> - find_next_bit
>> - find_next_zero_bit
>> - find_next_zero_area
>>
>> Should we move that into bitmap.c/bitmap.h ?
>
> Definitely! For my NUMA work I have also coded some bitmap functions.
> Since mine are not performance critical, I reverted from implementing
> set_bits and clear_bits and replaced them with a loop in the calling code.
> So I could just could come around with a macro only implementation, for
> which a header file suffices (attached for reference).
>
>> Which part of QEMU could
>> use that (block.c maybe ?)
>
> As mentioned, the yet to be submitted NUMA code would benefit from it. Linux
> has also bitmap code, maybe you could leverage this (if not already done).

Most of my code already comes from Linux. Then I'll try to create that
module and send a patch next week.

Thanks,
-- 
Corentin Chary
http://xf.iksaif.net