On 5/27/21 7:05 PM, Wang Jianchao wrote: > Does it really matter that issue IO request by the order of io priority ? > > Given a device with a 32 depth queue and doesn't support io priority, even if > we issue the request by the order of io priority, will the fw of device handle > them by the same order ? Or in the other word, we always issue 32 io requests > to device one time and then the fw of device decides how to handle them. > The order of dispatching request from queue may only work when the device's > queue is full and we have a deeper queue in io scheduler. And at this moment, > maybe the user needs to check why their application saturates the block device. > > As for the qos policy of io priority, it seems similar with wbt in which read, > sync write and background write have different priority. Since we always want > the io with higher priority to be served more by the device, adapting the depth > of queue of different io priority may work ;) Hi Jianchao, Our conclusion from the extensive measurements we ran is that we cannot reach our latency goals for high-priority I/O without I/O priority support in the storage device. This is why we are working with device vendors on implementing I/O priority support in the storage devices that matter to us. Thanks, Bart.
