Ok. Measurements vs. simple cmpxchg on a Intel(R) Pentium(R) 4 CPU 3.20GHz
(hyperthreading enabled). Test run with your module show only minor
performance improvements and lots of regressions. So we must have
cmpxchg_local to see any improvements? Some kind of a recent optimization
of cmpxchg performance that we do not see on older cpus?
Code of kmem_cache_alloc (to show you that there are no debug options on):
Dump of assembler code for function kmem_cache_alloc:
0x4015cfa9 <kmem_cache_alloc+0>: push %ebp
0x4015cfaa <kmem_cache_alloc+1>: mov %esp,%ebp
0x4015cfac <kmem_cache_alloc+3>: push %edi
0x4015cfad <kmem_cache_alloc+4>: push %esi
0x4015cfae <kmem_cache_alloc+5>: push %ebx
0x4015cfaf <kmem_cache_alloc+6>: sub $0x10,%esp
0x4015cfb2 <kmem_cache_alloc+9>: mov %eax,%esi
0x4015cfb4 <kmem_cache_alloc+11>: mov %edx,0xffffffe8(%ebp)
0x4015cfb7 <kmem_cache_alloc+14>: mov 0x4(%ebp),%eax
0x4015cfba <kmem_cache_alloc+17>: mov %eax,0xfffffff0(%ebp)
0x4015cfbd <kmem_cache_alloc+20>: mov %fs:0x404af008,%eax
0x4015cfc3 <kmem_cache_alloc+26>: mov 0x90(%esi,%eax,4),%edi
0x4015cfca <kmem_cache_alloc+33>: mov (%edi),%ecx
0x4015cfcc <kmem_cache_alloc+35>: test %ecx,%ecx
0x4015cfce <kmem_cache_alloc+37>: je 0x4015d00a <kmem_cache_alloc+97>
0x4015cfd0 <kmem_cache_alloc+39>: mov 0xc(%edi),%eax
0x4015cfd3 <kmem_cache_alloc+42>: mov (%ecx,%eax,4),%eax
0x4015cfd6 <kmem_cache_alloc+45>: mov %eax,%edx
0x4015cfd8 <kmem_cache_alloc+47>: mov %ecx,%eax
0x4015cfda <kmem_cache_alloc+49>: lock cmpxchg %edx,(%edi)
0x4015cfde <kmem_cache_alloc+53>: mov %eax,%ebx
0x4015cfe0 <kmem_cache_alloc+55>: cmp %ecx,%eax
0x4015cfe2 <kmem_cache_alloc+57>: jne 0x4015cfbd <kmem_cache_alloc+20>
0x4015cfe4 <kmem_cache_alloc+59>: cmpw $0x0,0xffffffe8(%ebp)
0x4015cfe9 <kmem_cache_alloc+64>: jns 0x4015d006 <kmem_cache_alloc+93>
0x4015cfeb <kmem_cache_alloc+66>: mov 0x10(%edi),%edx
0x4015cfee <kmem_cache_alloc+69>: xor %eax,%eax
0x4015cff0 <kmem_cache_alloc+71>: mov %edx,%ecx
0x4015cff2 <kmem_cache_alloc+73>: shr $0x2,%ecx
0x4015cff5 <kmem_cache_alloc+76>: mov %ebx,%edi
Base
1. Kmalloc: Repeatedly allocate then free test
10000 times kmalloc(8) -> 332 cycles kfree -> 422 cycles
10000 times kmalloc(16) -> 218 cycles kfree -> 360 cycles
10000 times kmalloc(32) -> 214 cycles kfree -> 368 cycles
10000 times kmalloc(64) -> 244 cycles kfree -> 390 cycles
10000 times kmalloc(128) -> 320 cycles kfree -> 417 cycles
10000 times kmalloc(256) -> 438 cycles kfree -> 550 cycles
10000 times kmalloc(512) -> 527 cycles kfree -> 626 cycles
10000 times kmalloc(1024) -> 678 cycles kfree -> 775 cycles
10000 times kmalloc(2048) -> 748 cycles kfree -> 822 cycles
10000 times kmalloc(4096) -> 641 cycles kfree -> 650 cycles
10000 times kmalloc(8192) -> 741 cycles kfree -> 817 cycles
10000 times kmalloc(16384) -> 872 cycles kfree -> 927 cycles
2. Kmalloc: alloc/free test
10000 times kmalloc(8)/kfree -> 332 cycles
10000 times kmalloc(16)/kfree -> 327 cycles
10000 times kmalloc(32)/kfree -> 323 cycles
10000 times kmalloc(64)/kfree -> 320 cycles
10000 times kmalloc(128)/kfree -> 320 cycles
10000 times kmalloc(256)/kfree -> 333 cycles
10000 times kmalloc(512)/kfree -> 332 cycles
10000 times kmalloc(1024)/kfree -> 330 cycles
10000 times kmalloc(2048)/kfree -> 334 cycles
10000 times kmalloc(4096)/kfree -> 674 cycles
10000 times kmalloc(8192)/kfree -> 1155 cycles
10000 times kmalloc(16384)/kfree -> 1226 cycles
Slub cmpxchg.
1. Kmalloc: Repeatedly allocate then free test
10000 times kmalloc(8) -> 296 cycles kfree -> 515 cycles
10000 times kmalloc(16) -> 193 cycles kfree -> 412 cycles
10000 times kmalloc(32) -> 188 cycles kfree -> 422 cycles
10000 times kmalloc(64) -> 222 cycles kfree -> 441 cycles
10000 times kmalloc(128) -> 292 cycles kfree -> 476 cycles
10000 times kmalloc(256) -> 414 cycles kfree -> 589 cycles
10000 times kmalloc(512) -> 513 cycles kfree -> 673 cycles
10000 times kmalloc(1024) -> 694 cycles kfree -> 825 cycles
10000 times kmalloc(2048) -> 739 cycles kfree -> 878 cycles
10000 times kmalloc(4096) -> 636 cycles kfree -> 653 cycles
10000 times kmalloc(8192) -> 715 cycles kfree -> 799 cycles
10000 times kmalloc(16384) -> 855 cycles kfree -> 927 cycles
2. Kmalloc: alloc/free test
10000 times kmalloc(8)/kfree -> 354 cycles
10000 times kmalloc(16)/kfree -> 336 cycles
10000 times kmalloc(32)/kfree -> 335 cycles
10000 times kmalloc(64)/kfree -> 337 cycles
10000 times kmalloc(128)/kfree -> 337 cycles
10000 times kmalloc(256)/kfree -> 355 cycles
10000 times kmalloc(512)/kfree -> 354 cycles
10000 times kmalloc(1024)/kfree -> 337 cycles
10000 times kmalloc(2048)/kfree -> 339 cycles
10000 times kmalloc(4096)/kfree -> 674 cycles
10000 times kmalloc(8192)/kfree -> 1128 cycles
10000 times kmalloc(16384)/kfree -> 1240 cycles
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