On 5/27/21 1:05 AM, Wang Jianchao wrote: > On 2021/5/27 2:25 PM, Wang Jianchao wrote: >> On 2021/5/27 9:01 AM, Bart Van Assche wrote: >>> A feature that is missing from the Linux kernel for storage devices that >>> support I/O priorities is to set the I/O priority in requests involving page >>> cache writeback. Since the identity of the process that triggers page cache >>> writeback is not known in the writeback code, the priority set by ioprio_set() >>> is ignored. However, an I/O cgroup is associated with writeback requests >>> by certain filesystems. Hence this patch series that implements the following >>> changes for the mq-deadline scheduler: >> >> How about implement this feature based on the rq-qos framework ? >> Maybe it is better to make mq-deadline a pure io-scheduler. > > In addition, it is more flexible to combine different io-scheduler and rq-qos policy > if we take io priority as a new policy ;) Hi Jianchao, That's an interesting question. I'm in favor of flexibility. However, I'm not sure whether it would be possible to combine an rq-qos policy that submits high priority requests first with an I/O scheduler that ignores I/O priorities. Since a typical I/O scheduler reorders requests, such a combination would lead to requests being submitted in the wrong order to storage devices. In other words, when using an I/O scheduler, proper support for I/O priority in the I/O scheduler is essential. The BFQ I/O scheduler is still maturing. The purpose of the Kyber I/O scheduler is to control latency by reducing the queue depth without differentiating between requests of the same type. The mq-deadline scheduler is already being used in combination with storage devices that support I/O priorities in their controller. Hence the choice for the mq-deadline scheduler. Thanks, Bart.
