Re: [PATCH,RFC] faster kmalloc lookup

[Manfred Spraul <manfred@colorfullife.com>]

I've run my slab microbenchmark over the 3 versions:
- current
- generic_fls
- i386 asm optimized fls

The test reports the fastest time for 100 kmalloc calls in a tight loop 
(Duron 700). Loop/test overhead substracted.

32-byte alloc:
current:        41 ticks
generic_fls: 56 ticks
bsrl:            54 ticks

4096 byte alloc: 84 ticks
generic_fls: 53 ticks
bsrl:        54 ticks

40 ticks difference for -current between 4096 and 32 bytes - ~4 cycles 
for each loop.
bit scan is 10 ticks slower for 32 byte allocs, 30 ticks faster for 4096 
byte allocs.

No difference between generic_fls and bsrl - the branch predictor can 
easily predict all branches in generic_fls for constant kmalloc calls.

--
    Manfred