On 1/10/24 2:05 AM, Xiaobing Li wrote: > On 1/5/24 04:02 AM, Pavel Begunkov wrote: >> On 1/3/24 05:49, Xiaobing Li wrote: >>> 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 >> >> How does taking a measure for task runtime looks like? I expect it to >> be a simple read of a variable inside task_struct, maybe with READ_ONCE, >> in which case the overhead shouldn't be realistically measurable. Does >> it need locking? > > The task runtime I am talking about is similar to this: > start = get_system_time(current); > do_io_part(); > sq->total_time += get_system_time(current) - start; Not sure what get_system_time() is, don't see that anywhere. > Currently, it is not possible to obtain the execution time of a piece of > code by a simple read of a variable inside task_struct. > Or do you have any good ideas? I must be missing something, because it seems like all you need is to read task->stime? You could possible even make do with just logging busy loop time, as getrusage(RUSAGE_THREAD, &stat) from userspace would then give you the total time. stat.ru_stime would then be the total time, the thread ran, and 1 - (above_busy_stime / stat.ru_stime) would give you the time the percentage of time the thread ran and did useful work (eg not busy looping. Hmm? -- Jens Axboe
