Hi Paolo! I have two processes doing direct IO writes like: dd if=/dev/zero of=/mnt/file$i bs=128k oflag=direct count=4000M Now each of these processes belongs to a different cgroup and it has different bfq.weight. I was looking into why these processes do not split bandwidth according to BFQ weights. Or actually the bandwidth is split accordingly initially but eventually degrades into 50/50 split. After some debugging I've found out that due to luck, one of the processes is decided to be a waker of the other process and at that point we loose isolation between the two cgroups. This pretty reliably happens sometime during the run of these two processes on my test VM. So can we tweak the waker logic to reduce the chances for false positives? Essentially when there are only two processes doing heavy IO against the device, the logic in bfq_check_waker() is such that they are very likely to eventually become wakers of one another. AFAICT the only condition that needs to get fulfilled is that they need to submit IO within 4 ms of the completion of IO of the other process 3 times. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
