On 12/30/23 9:27 AM, Pavel Begunkov wrote: > Why it uses jiffies instead of some task run time? > Consequently, why it's fine to account irq time and other > preemption? (hint, it's not) > > Why it can't be done with userspace and/or bpf? Why > can't it be estimated by checking and tracking > IORING_SQ_NEED_WAKEUP in userspace? > > What's the use case in particular? Considering that > one of the previous revisions was uapi-less, something > is really fishy here. Again, it's a procfs file nobody > but a few would want to parse to use the feature. > > Why it just keeps aggregating stats for the whole > life time of the ring? If the workload changes, > that would either totally screw the stats or would make > it too inert to be useful. That's especially relevant > for long running (days) processes. There should be a > way to reset it so it starts counting anew. Hi, Jens and Pavel, I carefully read the questions you raised. First of all, as to why I use jiffies to statistics time, it is because I have done some performance tests and found that using jiffies has a relatively smaller loss of performance than using task run time. Of course, using task run time is indeed more accurate. But in fact, our requirements for accuracy are not particularly high, so after comprehensive consideration, we finally chose to use jiffies. Of course, if you think that a little more performance loss here has no impact, I can use task run time instead, but in this case, does the way of calculating sqpoll thread timeout also need to be changed, because it is also calculated through jiffies. Then there’s how to use this metric. We are studying some optimization methods for io-uring, including performance and CPU utilization, but we found that there is currently no tool that can observe the CPU ratio of sqthread's actual processing IO part, so we want to merge this method that can observe this value so that we can more easily observe the optimization effects. Best regards, -- Xiaobing Li
