On Thu, Sep 09, 2021 at 08:00:24PM +0800, Huangzhaoyang wrote: > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > psi's memstall time is counted as simple as exit - entry so far, which ignore > the task's off cpu time. Fix it by calc the percentage of off time via task and > rq's util and runq load. > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> Can you please explain what practical problem you are trying to solve? If a reclaimer gets preempted and has to wait for CPU, should that stall be attributed to a lack of memory? Some of it should, since page reclaim consumed CPU budget that would've otherwise been available for doing real work. The application of course may still have experienced a CPU wait outside of reclaim, but potentially a shorter one. Memory pressure can definitely increase CPU pressure (as it can IO pressure). Proportional and transitive accounting - how much of total CPU load is page reclaim, and thus how much of each runq wait is due to memory pressure - would give more precise answers. But generally discounting off-CPU time in a stall is not any more correct than including it all. This is doable, but I think there needs to be better justification for providing this level of precision, since it comes with code complexity that has performance and maintenance overhead.
