Hello, I'm running into an issue which I don't know how to debug. So I'm open to ideas and suggestions :-) On my arm64 board, I have enabled Universal Flash Storage support. I wanted to benchmark read performance, and noticed that the system locks up when I read partitions larger than 3.5 GB, unless I tell dd to use direct IO: *** WITH O_DIRECT *** # dd if=/dev/sda of=/dev/null bs=1M iflag=direct status=progress 57892929536 bytes (58 GB, 54 GiB) copied, 697.006 s, 83.1 MB/s 55256+0 records in 55256+0 records out 57940115456 bytes (58 GB, 54 GiB) copied, 697.575 s, 83.1 MB/s *** WITHOUT O_DIRECT *** # dd if=/dev/sda of=/dev/null bs=1M status=progress 3853516800 bytes (3.9 GB, 3.6 GiB) copied, 49.0002 s, 78.6 MB/s rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...0: (8242 ticks this GP) idle=106/1/0x4000000000000000 softirq=168/171 fqs=2626 rcu: 6-...0: (99 GPs behind) idle=ec2/1/0x4000000000000000 softirq=71/71 fqs=2626 rcu: (detected by 7, t=5254 jiffies, g=-275, q=2) Task dump for CPU 1: kworker/1:1H R running task 0 675 2 0x0000002a Workqueue: kblockd blk_mq_run_work_fn Call trace: __switch_to+0x168/0x1d0 0xffffffc0f6efbbc8 blk_mq_run_work_fn+0x28/0x40 process_one_work+0x208/0x470 worker_thread+0x48/0x460 kthread+0x128/0x130 ret_from_fork+0x10/0x1c Task dump for CPU 6: kthreadd R running task 0 2 0 0x0000002a Call trace: __switch_to+0x168/0x1d0 0x5b36396f4e7d4000 rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 1-...0: (8242 ticks this GP) idle=106/1/0x4000000000000000 softirq=168/171 fqs=10500 rcu: 6-...0: (99 GPs behind) idle=ec2/1/0x4000000000000000 softirq=71/71 fqs=10500 rcu: (detected by 7, t=21009 jiffies, g=-275, q=2) Task dump for CPU 1: kworker/1:1H R running task 0 675 2 0x0000002a Workqueue: kblockd blk_mq_run_work_fn Call trace: __switch_to+0x168/0x1d0 0xffffffc0f6efbbc8 blk_mq_run_work_fn+0x28/0x40 process_one_work+0x208/0x470 worker_thread+0x48/0x460 kthread+0x128/0x130 ret_from_fork+0x10/0x1c Task dump for CPU 6: kthreadd R running task 0 2 0 0x0000002a Call trace: __switch_to+0x168/0x1d0 0x5b36396f4e7d4000 The system always hangs around the 3.6 GiB mark, wherever I start from. How can I debug this issue? Regards.
