: >> 400480: f3 90 pause >> 400482: c3 retq >> 400483: 90 nop >> >> ... >> >> Case3 - asm volitile("rep;pause" ::: "memory") >> 0000000000400480

: >> 400480: f3 f3 90 pause >> 400483: c3 retq >> 400484: 90 nop >> _______ >> Note the difference between opcodes case 1 and case 3, and the mess >> made by the compiler in case 2. >> >> As to benchmarks - I've checked a few things, no formal or lasting >> stuff... but striking at first glance: >> >> 1) At idle, perf top shows time spent in _raw_spin_lock dropping from >> ~35% to ~25%. >> 2) Running a media transcode (single core - handbrakecli): frame rate >> increased by about 5-10%. >> 3) During file-intensive operations (#2, above, or copying large >> files - ext4 on software raid6) - latencytop shows a decerase on >> writing a page to disc from about 120ms to about 90ms. >> > Disregard case 2 - was missing -O3. With -O3 or -O2 rep;nop and pause > are identical. The interesting case is rep;pause which is different > and seems more efficient. Just to move away from this... totally perplexed, I retested a bit. Seems something else had gone wrong causing me to try 'rep;pause' vs. 'pause'. The resulting opcode is f3 f3 90, as noted above. I do see what seems to be a small but noticeable performance improvement - no idea if there's a downside, and also no idea what f3 f3 90 does vs. f3 90. Might be something interesting, or maybe not. Test scenario: Boot clean to single user mode. perform tiotest -8 five times. %cpu is %usr + %sys as reported by tiotest. Results: Writes pause: 1.14 sec; 72.01MB/sec; 322.44%cpu rep;pause: 1.12 sec; 70.4MB/sec; 311.58%cpu Random Writes pause: 3.7 sec; 8.51MB/sec; 66.48%cpu rep;pause 3.46sec; 9.04MB/sec; 72.34%cpu Reads pause: 11557.48MB/sec; 6040.74%cpu rep;pause 11620.15MB/sec; 5974.90%cpu Random Reads pause: 11416.9MB/sec; 5330.50%cpu rep;pause 11786.99MB/sec; 5118.66%cpu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/