On 5/26/20 7:57 AM, Hamilton Tobon Mosquera wrote: > Thank you for your answer. > > This is how I'm making sure that it is polling. The workloads take 2 > minutes, I'm checking the interrupts registered in /proc/interrupts for > the nvme device (the Intel Optane) when the workload starts and when the > workload ends. The interrupts count is almost zero, about 25 or so, > while when using an interrupt based engine I get about 600K interrupts. > > Also, the way I'm loading the nvme driver is: > > modprobe nvme poll_queues=4 > > As you said I'm using 4 polling queues because I only have 4 physical > cores. To check that they were actually created I use: > > systool -vm nvme > > Which shows that effectively there are 4 polling queues created. > > I also checked the file /sys/block/nvme0n1/queue/io_poll and it is set > to 1. Sometimes I change the file /sys/block/nvme0n1/queue/io_poll_delay > to switch between hybrid and normal polling and it shows differences in > the CPU usage, the latencies, IOPS, ... > > Another way is by checking the CPU usage, which says that the CPU is > almost completely occupied when polling. > > Also, I tried with dmesg as you suggested and this is the output: > > [627676.640431] nvme nvme0: 4/0/4 default/read/poll queues > > I guess that shows that I was effectively using polling in the > workloads. What is weird is that when I don't use the flag HIPRI it runs > ok but using interrupts not polling. It might be important to say that > I'm always running with root user. > > Does this information give you more hints about the problem?. Could you > please tell me in what filesystem polling is known to work 100% of the > time?. > > Thank you for your help. You did the right thing on the NVMe side, I'm guessing then that it's ext4 again. What kernel are you using? I think only 5.7 and newer supports polling on ext4, you'll have better luck with XFS. And btw, please don't top-post. Reply with proper quoting, top posting totally messes up the flow of conversation. -- Jens Axboe
