On Sun, Mar 21, 2021 at 11:14:32AM +1300, Barry Song wrote:
update_idle_core() is only done for the case of sched_smt_present. but test_idle_cores() is done for all machines even those without smt. this could contribute to up 8%+ hackbench performance loss on a machine like kunpeng 920 which has no smt. this patch removes the redundant test_idle_cores() for non-smt machines.
we run the below hackbench with different -g parameter from 2 to 14, for each different g, we run the command 10 times and get the average time: $ numactl -N 0 hackbench -p -T -l 20000 -g $1
hackbench will report the time which is needed to complete a certain number of messages transmissions between a certain number of tasks, for example: $ numactl -N 0 hackbench -p -T -l 20000 -g 10 Running in threaded mode with 10 groups using 40 file descriptors each (== 400 tasks) Each sender will pass 20000 messages of 100 bytes
The below is the result of hackbench w/ and w/o this patch: g= 2 4 6 8 10 12 14 w/o: 1.8151 3.8499 5.5142 7.2491 9.0340 10.7345 12.0929 w/ : 1.8428 3.7436 5.4501 6.9522 8.2882 9.9535 11.3367 +4.1% +8.3% +7.3% +6.3%
Signed-off-by: Barry Song song.bao.hua@hisilicon.com
Acked-by: Mel Gorman mgorman@suse.de
That said, the numa_idle_core() function then becomes slightly redundant. A possible follow up is to move the "idle_core >= 0" check in numa_idle_core() to its caller in update_numa_stats() and then remove the redundant check in !static_branch_likely(&sched_smt_present) check in numa_idle_core.