Re: [PATCH 0/3] fix interrupt swamp in NVMe

[Ming Lei]

On Thu, Aug 22, 2019 at 10:00 AM Keith Busch <keith.busch@xxxxxxxxx> wrote:
>
> On Wed, Aug 21, 2019 at 7:34 PM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> > On Wed, Aug 21, 2019 at 04:27:00PM +0000, Long Li wrote:
> > > Here is the command to benchmark it:
> > >
> > > fio --bs=4k --ioengine=libaio --iodepth=128 --filename=/dev/nvme0n1:/dev/nvme1n1:/dev/nvme2n1:/dev/nvme3n1:/dev/nvme4n1:/dev/nvme5n1:/dev/nvme6n1:/dev/nvme7n1:/dev/nvme8n1:/dev/nvme9n1 --direct=1 --runtime=120 --numjobs=80 --rw=randread --name=test --group_reporting --gtod_reduce=1
> > >
> >
> > I can reproduce the issue on one machine(96 cores) with 4 NVMes(32 queues), so
> > each queue is served on 3 CPUs.
> >
> > IOPS drops > 20% when 'use_threaded_interrupts' is enabled. From fio log, CPU
> > context switch is increased a lot.
>
> Interestingly use_threaded_interrupts shows a marginal improvement on
> my machine with the same fio profile. It was only 5 NVMes, but they've
> one queue per-cpu on 112 cores.

Not investigate it yet.

BTW, my fio test is only done on the single hw queue via 'taskset -c
$cpu_list_of_the_queue',
without applying the threaded interrupt affinity patch. NVMe is Optane.

The same issue can be reproduced after I force to use 1:1 mapping via passing
'possible_cpus=32' kernel cmd line.

Maybe related with kernel options, so attache the one I used, and
basically it is
a subset of RHEL8 kernel.

Thanks,
Ming Lei

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