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Comparing libev/ev_iouring.c (file contents):
Revision 1.5 by root, Tue Nov 19 13:09:00 2019 UTC vs.
Revision 1.7 by root, Sun Dec 22 15:05:32 2019 UTC

… …
47 * without any syscalls. what's not to like? 47 * without any syscalls. what's not to like?
48 * d) ok, it's vastly more complex, but that's ok, really. 48 * d) ok, it's vastly more complex, but that's ok, really.
49 * e) why 3 mmaps instead of one? one would be more space-efficient, 49 * e) why 3 mmaps instead of one? one would be more space-efficient,
50 * and I can't see what benefit three would have (other than being 50 * and I can't see what benefit three would have (other than being
51 * somehow resizable/relocatable, but that's apparently not possible). 51 * somehow resizable/relocatable, but that's apparently not possible).
52 * (FIXME: newer kernels can use 2 mmaps only, need to look into this).
52 * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and 53 * f) hmm, it's practiclaly undebuggable (gdb can't access the memory, and
53 the bizarre way structure offsets are commuinicated makes it hard to 54 * the bizarre way structure offsets are communicated makes it hard to
54 * just print the ring buffer heads, even *iff* the memory were visible 55 * just print the ring buffer heads, even *iff* the memory were visible
55 * in gdb. but then, that's also ok, really. 56 * in gdb. but then, that's also ok, really.
56 * g) well, you cannot specify a timeout when waiting for events. no, 57 * g) well, you cannot specify a timeout when waiting for events. no,
57 * seriously, the interface doesn't support a timeout. never seen _that_ 58 * seriously, the interface doesn't support a timeout. never seen _that_
58 * before. sure, you can use a timerfd, but that's another syscall 59 * before. sure, you can use a timerfd, but that's another syscall
59 * you could have avoided. overall, this bizarre omission smells 60 * you could have avoided. overall, this bizarre omission smells
60 * like a µ-optimisation by the io_uring author for his personal 61 * like a µ-optimisation by the io_uring author for his personal
61 * applications, to the detriment of everybody else who just wants 62 * applications, to the detriment of everybody else who just wants
62 * an event loop. but, umm, ok, if that's all, it could be worse. 63 * an event loop. but, umm, ok, if that's all, it could be worse.
64 * (FIXME: jens mentioned timeout commands, need to investigate)
63 * h) there is a hardcoded limit of 4096 outstanding events. okay, 65 * h) there is a hardcoded limit of 4096 outstanding events. okay,
64 * at least there is no arbitrary low system-wide limit... 66 * at least there is no arbitrary low system-wide limit...
67 * (FIXME: apparently, this was increased to 32768 in later kernels(
65 * i) unlike linux aio, you *can* register more then the limit 68 * i) unlike linux aio, you *can* register more then the limit
66 * of fd events, and the kernel will "gracefully" signal an 69 * of fd events, and the kernel will "gracefully" signal an
67 * overflow, after which you could destroy and recreate the kernel 70 * overflow, after which you could destroy and recreate the kernel
68 * state, a bit bigger, or fall back to e.g. poll. thats not 71 * state, a bit bigger, or fall back to e.g. poll. thats not
69 * totally insane, but kind of questions the point a high 72 * totally insane, but kind of questions the point a high
70 * performance I/O framework when it doesn't really work 73 * performance I/O framework when it doesn't really work
71 * under stress. 74 * under stress.
75 * (FIXME: iouring should no longer drop events, need to investigate)
72 * j) but, oh my! is has exactly the same bugs as the linux aio backend, 76 * j) but, oh my! is has exactly the same bugs as the linux aio backend,
73 * where some undocumented poll combinations just fail. 77 * where some undocumented poll combinations just fail.
74 * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course, 78 * so we need epoll AGAIN as a fallback. AGAIN! epoll!! and of course,
75 * this is completely undocumented, have I mantioned this already? 79 * this is completely undocumented, have I mantioned this already?
76 * k) overall, the *API* itself is, I dare to say, not a total trainwreck. 80 * k) overall, the *API* itself is, I dare to say, not a total trainwreck.
… …
576 timeout = EV_TS_CONST (0.); 580 timeout = EV_TS_CONST (0.);
577 else 581 else
578 /* no events, so maybe wait for some */ 582 /* no events, so maybe wait for some */
579 iouring_tfd_update (EV_A_ timeout); 583 iouring_tfd_update (EV_A_ timeout);
580 584
581 /* only enter the kernel if we have somethign to submit, or we need to wait */ 585 /* only enter the kernel if we have something to submit, or we need to wait */
582 if (timeout || iouring_to_submit) 586 if (timeout || iouring_to_submit)
583 { 587 {
584 int res; 588 int res;
585 589
586 EV_RELEASE_CB; 590 EV_RELEASE_CB;
… …
606iouring_init (EV_P_ int flags) 610iouring_init (EV_P_ int flags)
607{ 611{
608 if (!epoll_init (EV_A_ 0)) 612 if (!epoll_init (EV_A_ 0))
609 return 0; 613 return 0;
610 614
615 iouring_entries = IOURING_INIT_ENTRIES;
616 iouring_max_entries = 0;
617
618 if (iouring_internal_init (EV_A) < 0)
619 {
620 iouring_internal_destroy (EV_A);
621 return 0;
622 }
623
611 ev_io_init (&iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ); 624 ev_io_init (&iouring_epoll_w, iouring_epoll_cb, backend_fd, EV_READ);
612 ev_set_priority (&iouring_epoll_w, EV_MAXPRI); 625 ev_set_priority (&iouring_epoll_w, EV_MAXPRI);
613 626
614 ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ); 627 ev_io_init (&iouring_tfd_w, iouring_tfd_cb, iouring_tfd, EV_READ);
615 ev_set_priority (&iouring_tfd_w, EV_MAXPRI); 628 ev_set_priority (&iouring_tfd_w, EV_MAXPRI);
616
617 iouring_entries = IOURING_INIT_ENTRIES;
618 iouring_max_entries = 0;
619
620 if (iouring_internal_init (EV_A) < 0)
621 {
622 iouring_internal_destroy (EV_A);
623 return 0;
624 }
625 629
626 ev_io_start (EV_A_ &iouring_epoll_w); 630 ev_io_start (EV_A_ &iouring_epoll_w);
627 ev_unref (EV_A); /* watcher should not keep loop alive */ 631 ev_unref (EV_A); /* watcher should not keep loop alive */
628 632
629 ev_io_start (EV_A_ &iouring_tfd_w); 633 ev_io_start (EV_A_ &iouring_tfd_w);

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