On 2023/3/29 18:52, Ming Lei wrote: > On Wed, Mar 29, 2023 at 06:01:16PM +0800, Ziyang Zhang wrote: >> On 2023/3/29 17:00, Ming Lei wrote: >>> On Wed, Mar 29, 2023 at 10:57:53AM +0800, Ziyang Zhang wrote: >>>> On 2023/3/28 23:09, Ming Lei wrote: >>>>> Apply io_uring fused command for supporting zero copy: >>>>> >>>> >>>> [...] >>>> >>>>> >>>>> @@ -1374,7 +1533,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) >>>>> if (!ubq || ub_cmd->q_id != ubq->q_id) >>>>> goto out; >>>>> >>>>> - if (ubq->ubq_daemon && ubq->ubq_daemon != current) >>>>> + /* >>>>> + * The fused command reads the io buffer data structure only, so it >>>>> + * is fine to be issued from other context. >>>>> + */ >>>>> + if ((ubq->ubq_daemon && ubq->ubq_daemon != current) && >>>>> + (cmd_op != UBLK_IO_FUSED_SUBMIT_IO)) >>>>> goto out; >>>>> >>>> >>>> Hi Ming, >>>> >>>> What is your use case that fused io_uring cmd is issued from another thread? >>>> I think it is good practice to operate one io_uring instance in one thread >>>> only. >>> >>> So far we limit io command has to be issued from the queue context, >>> which is still not friendly from userspace viewpoint, the reason is >>> that we can't get io_uring exit notification and ublk's use case is >>> very special since the queued io command may not be completed forever, >> >> OK, so UBLK_IO_FUSED_SUBMIT_IO is guaranteed to be completed because it is >> not queued. FETCH_REQ and COMMIT_AMD_FETCH are queued io commands and could >> not be completed forever so they have to be issued from ubq_daemon. Right? > > Yeah, any io command should be issued from ubq daemon context. > >> >> BTW, maybe NEED_GET_DATA can be issued from other context... > > So far it won't be supported. > > As I mentioned in the link, if io_uring can provide io_uring exit > callback, we may relax this limit. > Hi, Ming Sorry, I do not understand... I think UBLK_IO_NEED_GET_DATA is normal IO just like UBLK_IO_FUSED_SUBMIT_IO. It is issued from one pthread(ubq_daemon for now) and is completed just in time(not queued). So I think we can allow UBLK_IO_NEED_GET_DATA to be issued from other context.
