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SubjectRe: slab: avoid linear search in kmalloc? (GCC Guru wanted :)
Bernd Eckenfels wrote:
>
> Hello,
>
> I noticed that kmalloc and kmem_find_general_cachep are doing a linear
> search in the cache_sizes array. Isnt it better to speed that up by doing a
> binary search or a b-tree if like the following patch?
>

Possibly. I've never seen it on a profile though.

Just for kicks, try feeding this into gcc and take a look
at the assembly output:

int thing(int size)
{
int ret;

switch (size) {
case 0 ... 2:
return 1;
case 3 ... 4:
return 2;
case 5 ... 8:
return 3;
case 9 ... 16:
return 4;
case 17 ... 31:
return 5;
case 32 ... 64:
return 6;
case 65 ... 128:
return 7;
case 129 ... 256:
return 8;
case 257 ... 512:
return 9;
case 513 ... 1024:
return 10;
case 1025 ... 2048:
return 11;
case 2049 ... 4096:
return 12;
case 4097 ... 8192:
return 13;
case 8193 ... 16384:
return 14;
case 16385 ... 32768:
return 15;
case 32769 ... 65536:
return 16;
}
return -1;
}
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