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 09:28:07 -0600 |
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On 05/08/2017 09:24 AM, Will Deacon wrote: > On Mon, May 08, 2017 at 08:08:55AM -0600, Jens Axboe wrote: >> 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: >>>> 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. > > On my setup, doing this restored a bunch of the performance, but the numbers > are still ~5% worse than 4.10 (as opposed to ~20% worse with mq-deadline). > Disabling NUMA as well cuts this down to ~2%.
So we're down to 2%. How stable are these numbers? With mq-deadline attached, I'm not surprised there's a drop for a null_blk type of test.
Maybe a perf profile comparison between the two kernels would help?
-- Jens Axboe
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