Comment 19 for bug 1898786

Performing verification for Focal.

Since Benjamin hasn't responded, I will try and verify the best I can.

I made a instance on AWS. I used a c5d.large instance type, and added 8gb extra EBS storage.

I installed the latest kernel from -updates to get a performance baseline. kernel is 5.4.0-54-generic.

I made a bcache disk with the following.

Note, the 8gb disk was used as the cache disk, and the 50gb disk the backing disk. Having the cache small is to try force cache evictions often, and possibly try trigger the bug.

$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
nvme2n1 259:0 0 46.6G 0 disk
nvme1n1 259:1 0 8G 0 disk
nvme0n1 259:2 0 8G 0 disk
└─nvme0n1p1 259:3 0 8G 0 part /

$ sudo apt install bcache-tools
$ sudo dd if=/dev/zero if=/dev/nvme1n1 bs=512 count=8
$ sudo dd if=/dev/zero if=/dev/nvme2n1 bs=512 count=8
$ sudo wipefs -a /dev/nvme1n1
$ sudo wipefs -a /dev/nvme2n1
$ sudo make-bcache -C /dev/nvme1n1 -B /dev/nvme2n1
UUID: 3f28ca5d-856b-42e9-bbb7-54cae12b5538
Set UUID: 756747bc-f27c-44ca-a9b9-dbd132722838
version: 0
nbuckets: 16384
block_size: 1
bucket_size: 1024
nr_in_set: 1
nr_this_dev: 0
first_bucket: 1
UUID: cc3e36fd-3694-4c50-aeac-0b79d2faab4a
Set UUID: 756747bc-f27c-44ca-a9b9-dbd132722838
version: 1
block_size: 1
data_offset: 16
$ sudo mkfs.ext4 /dev/bcache0
$ sudo mkdir /media/bcache
$ sudo mount /dev/bcache0 /media/bcache
$ echo "/dev/bcache0 /media/bcache ext4 rw 0 0" | sudo tee -a /etc/fstab

From there, I installed fio to do some benchmarks, and to try apply some IO pressure to the cache.

$ sudo apt install fio

I used the following fio jobfile:

https://paste.ubuntu.com/p/RNBmXdy3zG/

It is based on the ssd test in: https://github.com/axboe/fio/blob/master/examples/ssd-test.fio

Running the fio job gives us the following output:

https://paste.ubuntu.com/p/HrWGNDJPfv/

Now we have the baseline, I enabled -proposed and installed 5.4.0-55-generic and rebooted.

I started the fio job again, and got the following output:

# uname -rv
5.4.0-55-generic #61-Ubuntu SMP Mon Nov 9 20:49:56 UTC 2020

https://paste.ubuntu.com/p/pDVXnspmvs/

If you compare the two outputs, there really isn't much difference in latencies / read / write speeds. The bcache patches don't seem to cause any large impacts.

I managed to set up a bcache disk, and did some IO stress tests. Things seem to be okay.

Since we had positive test results on the test kernel on the Launchpad git server, and the above shows we don't appear to have any regressions, I will mark this bug as verified for Focal.