* Christoph Lameter ([EMAIL PROTECTED]) wrote: > On Tue, 21 Aug 2007, Mathieu Desnoyers wrote: > > > SLUB Use cmpxchg() everywhere. > > > > It applies to "SLUB: Single atomic instruction alloc/free using > > cmpxchg". > > > +++ slab/mm/slub.c 2007-08-20 18:42:28.000000000 -0400 > > @@ -1682,7 +1682,7 @@ redo: > > > > object[c->offset] = freelist; > > > > - if (unlikely(cmpxchg_local(&c->freelist, freelist, object) != freelist)) > > + if (unlikely(cmpxchg(&c->freelist, freelist, object) != freelist)) > > goto redo; > > return; > > slow: > > Ok so regular cmpxchg, no cmpxchg_local. cmpxchg_local does not bring > anything more? My measurements did not show any difference. I measured on > Athlon64. What processor is being used? >
This patch only cleans up the tree before proposing my cmpxchg_local changes. There was an inconsistent use of cmpxchg/cmpxchg_local there. Using cmpxchg_local vs cmpxchg has a clear impact on the fast paths, as shown below: it saves about 60 to 70 cycles for kmalloc and 200 cycles for the kmalloc/kfree pair (test 2). Pros : - we can use barrier() instead of rmb() - cmpxchg_local is faster Con : - we must disable preemption I use a 3GHz Pentium 4 for my tests. Results (compared to cmpxchg_local numbers) : SLUB Performance testing ======================== 1. Kmalloc: Repeatedly allocate then free test (kfree here is slow path) * cmpxchg kmalloc(8) = 271 cycles kfree = 645 cycles kmalloc(16) = 158 cycles kfree = 428 cycles kmalloc(32) = 153 cycles kfree = 446 cycles kmalloc(64) = 178 cycles kfree = 459 cycles kmalloc(128) = 247 cycles kfree = 481 cycles kmalloc(256) = 363 cycles kfree = 605 cycles kmalloc(512) = 449 cycles kfree = 677 cycles kmalloc(1024) = 626 cycles kfree = 810 cycles kmalloc(2048) = 681 cycles kfree = 869 cycles kmalloc(4096) = 471 cycles kfree = 575 cycles kmalloc(8192) = 666 cycles kfree = 747 cycles kmalloc(16384) = 736 cycles kfree = 853 cycles * cmpxchg_local kmalloc(8) = 83 cycles kfree = 363 cycles kmalloc(16) = 85 cycles kfree = 372 cycles kmalloc(32) = 92 cycles kfree = 377 cycles kmalloc(64) = 115 cycles kfree = 397 cycles kmalloc(128) = 179 cycles kfree = 438 cycles kmalloc(256) = 314 cycles kfree = 564 cycles kmalloc(512) = 398 cycles kfree = 615 cycles kmalloc(1024) = 573 cycles kfree = 745 cycles kmalloc(2048) = 629 cycles kfree = 816 cycles kmalloc(4096) = 473 cycles kfree = 548 cycles kmalloc(8192) = 659 cycles kfree = 745 cycles kmalloc(16384) = 724 cycles kfree = 843 cycles 2. Kmalloc: alloc/free test *cmpxchg kmalloc(8)/kfree = 321 cycles kmalloc(16)/kfree = 308 cycles kmalloc(32)/kfree = 311 cycles kmalloc(64)/kfree = 310 cycles kmalloc(128)/kfree = 306 cycles kmalloc(256)/kfree = 325 cycles kmalloc(512)/kfree = 324 cycles kmalloc(1024)/kfree = 322 cycles kmalloc(2048)/kfree = 309 cycles kmalloc(4096)/kfree = 678 cycles kmalloc(8192)/kfree = 1027 cycles kmalloc(16384)/kfree = 1204 cycles * cmpxchg_local kmalloc(8)/kfree = 112 cycles kmalloc(16)/kfree = 103 cycles kmalloc(32)/kfree = 103 cycles kmalloc(64)/kfree = 103 cycles kmalloc(128)/kfree = 112 cycles kmalloc(256)/kfree = 111 cycles kmalloc(512)/kfree = 111 cycles kmalloc(1024)/kfree = 111 cycles kmalloc(2048)/kfree = 121 cycles kmalloc(4096)/kfree = 650 cycles kmalloc(8192)/kfree = 1042 cycles kmalloc(16384)/kfree = 1149 cycles -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
