On 5/6/21 1:20 PM, Hao Xu wrote: > 在 2021/5/7 上午1:10, Jens Axboe 写道: >> On 5/6/21 8:33 AM, Hao Xu wrote: >>> Users may want a higher priority for sq_thread or io-worker. Provide a >>> way to change the nice value(for SCHED_NORMAL) or scheduling policy. >> >> Silly question - why is this needed for sqpoll? With the threads now >> being essentially user threads, why can't we just modify nice and >> scheduler class from userspace instead? That should work now. I think >> this is especially true for sqpoll where it's persistent, and argument >> could be made for the io-wq worker threads that we'd need io_uring >> support for that, as they come and go and there's no reliable way to >> find and tweak the thread scheduler settings for that particular use >> case. >> >> It may be more convenient to support this through io_uring, and that is >> a valid argument. I do think that the better way would then be to simply >> pass back the sqpoll pid after ring setup, because then it'd almost be >> as simple to do it from the app itself using the regular system call >> interfaces for that. >> > Hi Jens, > It's my bad. I didn't realize this until I almost completed the patch, > then I looked into io_uring_param, found just __u32 resv[3] can be > leveraged. Not sure if it's neccessary to occupy one to do this, so I > still sent this patch for comments. >> In summary, I do think this _may_ make sense for the worker threads, >> being able to pass in this information and have io-wq worker thread >> setup perform the necessary tweaks when a thread is created, but it does > I'm working on this(for the io-wq worker), have done part of it. >> seem a bit silly to add this for sqpoll where it could just as easily be >> achieved from the application itself without needing to add this > It's beyond my knowledge, correct me if I'm wrong: if we do > it from application, we have to search the pid of sq_thread by it's name > which is iou-sqp-`sqd->task_pid`, and may be cut off because of > TASK_COMM_LEN(would this macro value be possibly changed in the > future?). And set_task_comm() is called when sq_thread runs, so there is > very small chance(but there is) that set_task_comm() hasn't been called > when application try to get the command name of sq_thread. Based on this > (if it is not wrong...) I think return pid of sq_thread in io_uring > level may be a better choice. Right, as mentioned in my email, we'd want to return the pid to both make it easier and reliable to perform this action for the sqpoll thread. Otherwise it's a bit of a mess in the application with having to look it up, even if we enure we set task comm before the thread is live. Having to lookup through that is very ugly, and I would not want the application to do that. But returning the pid would be a trivial change... We already copy the params back, we can just stuff it in there. Either as a new member, or re-use one of the existing sqthread members as they don't return any information currently. -- Jens Axboe
