* Mathieu Desnoyers ([EMAIL PROTECTED]) wrote: > Ok, I played with your patch a bit, and the results are quite > interesting: > ... > Summary: > > (tests repeated 10000 times on a 3GHz Pentium 4) > (kernel DEBUG menuconfig options are turned off) > results are in cycles per iteration > I did 2 runs of the slab.git HEAD to have an idea of errors associated > to the measurements: > > | slab.git HEAD slub (min-max) | cmpxchg_local slub > kmalloc(8) | 190 - 201 | 83 > kfree(8) | 351 - 351 | 363 > kmalloc(64) | 224 - 245 | 115 > kfree(64) | 389 - 394 | 397 > kmalloc(16384)| 713 - 741 | 724 > kfree(16384) | 843 - 856 | 843 > > Therefore, there seems to be a repeatable gain on the kmalloc fast path > (more than twice faster). No significant performance hit for the kfree > case, but no gain neither, same for large kmalloc, as expected. >
Having no performance improvement for kfree seems a little weird, since we are moving from irq disable to cmpxchg_local in the fast path. A possible explanation would be that we are always hitting the slow path. I did a simple test, counting the number of fast vs slow paths with my cmpxchg_local slub version: (initial state before the test) [ 386.359364] Fast slub free: 654982 [ 386.369507] Slow slub free: 392195 [ 386.379660] SLUB Performance testing [ 386.390361] ======================== [ 386.401020] 1. Kmalloc: Repeatedly allocate then free test ... (after test 1) [ 387.366002] Fast slub free: 657338 diff (2356) [ 387.376158] Slow slub free: 482162 diff (89967) [ 387.386294] 2. Kmalloc: alloc/free test ... (after test 2) [ 387.897816] Fast slub free: 748968 (diff 91630) [ 387.907947] Slow slub free: 482584 diff (422) Therefore, in the test where we have separate passes for slub allocation and free, we hit mostly the slow path. Any particular reason for that ? Note that the alloc/free test (test 2) seems to hit the fast path as expected. Mathieu -- 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/
