Hello, On Thu, Jun 01, 2023 at 01:39:19PM +0800, chengming.zhou@xxxxxxxxx wrote: > From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> > > iocost rely on rq start_time_ns and alloc_time_ns to tell the saturation > state of the block device. > > If any qos ->throttle() end up blocking, the cached rq start_time_ns and > alloc_time_ns will include its throtted time, which can confuse its user. I don't follow. rq_qos_throttle() happens before a request is allocated, so whether ->throttle() blocks or not doesn't affect alloc_time_ns or start_time_ns. > This patch add nr_flush counter in blk_plug, so we can tell if the task > has throttled in any qos ->throttle(), in which case we need to correct > the rq start_time_ns and alloc_time_ns. > > Another solution may be make rq_qos_throttle() return bool to indicate > if it has throttled in any qos ->throttle(). But this need more changes. > > Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> Depending on the flush behavior and adjusting alloc_time_ns seems fragile to me and will likely confuse other users of alloc_time_ns too. Maybe I'm misunderstanding the problem you're describing. Can you give a concrete example of how the current code would misbehave? Thanks. -- tejun
