Messages in this thread | | | Subject | Re: FIO performance regression in 4.11 kernel vs. 4.10 kernel observed on ARM64 | From | Jens Axboe <> | Date | Mon, 8 May 2017 08:08:55 -0600 |
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On 05/08/2017 05:19 AM, Arnd Bergmann wrote: > On Mon, May 8, 2017 at 1:07 PM, Will Deacon <will.deacon@arm.com> wrote: >> Hi Scott, >> >> Thanks for the report. >> >> On Fri, May 05, 2017 at 06:37:55PM -0700, Scott Branden wrote: >>> I have updated the kernel to 4.11 and see significant performance >>> drops using fio-2.9. >>> >>> Using FIO the performanced drops from 281 KIOPS to 207 KIOPS using >>> single core and task. >>> Percent performance drop becomes even worse if multi-cores and multi- >>> threads are used. >>> >>> Platform is ARM64 based A72. Can somebody reproduce the results or >>> know what may have changed to make such a dramatic change? >>> >>> FIO command and resulting log output below using null_blk to remove >>> as many hardware specific driver dependencies as possible. >>> >>> modprobe null_blk queue_mode=2 irqmode=0 completion_nsec=0 >>> submit_queues=1 bs=4096 >>> >>> taskset 0x1 fio --randrepeat=1 --ioengine=libaio --direct=1 --numjobs=1 >>> --gtod_reduce=1 --name=readtest --filename=/dev/nullb0 --bs=4k >>> --iodepth=128 --time_based --runtime=15 --readwrite=read >> >> I can confirm that I also see a ~20% drop in results from 4.10 to 4.11 on >> my AMD Seattle board w/ defconfig, but I can't see anything obvious in the >> log. >> >> Things you could try: >> >> 1. Try disabling CONFIG_NUMA in the 4.11 kernel (this was enabled in >> defconfig between the releases). >> >> 2. Try to reproduce on an x86 box >> >> 3. Have a go at bisecting the issue, so we can revert the offender if >> necessary. > > One more thing to try early: As 4.11 gained support for blk-mq I/O > schedulers compared to 4.10, null_blk will now also need some extra > cycles for each I/O request. Try loading the driver with "queue_mode=0" > or "queue_mode=1" instead of "queue_mode=2".
Since you have 1 submit queues set, you are being loaded with deadline attached. To compare 4.10 and 4.11, with queue_mode=2 and submit_queues=1, after loading null_blk in 4.11, do:
# echo none > /sys/block/nullb0/queue/scheduler
and re-test.
-- Jens Axboe
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