On Thu, 01/08 18:24, Andy Lutomirski wrote:
> On Thu, Jan 8, 2015 at 5:52 PM, Fam Zheng <f...@redhat.com> wrote:
> > On Thu, 01/08 17:28, Andy Lutomirski wrote:
> >> On Thu, Jan 8, 2015 at 5:25 PM, Fam Zheng <f...@redhat.com> wrote:
> >> > On Thu, 01/08 09:57, Andy Lutomirski wrote:
> >> >> I'd like to see a more ambitious change, since the timer isn't the
> >> >> only problem like this. Specifically, I'd like a syscall that does a
> >> >> list of epoll-related things and then waits. The list of things could
> >> >> include, at least:
> >> >>
> >> >> - EPOLL_CTL_MOD actions: level-triggered epoll users are likely to
> >> >> want to turn on and off their requests for events on a somewhat
> >> >> regular basis.
> >> >
> >> > This sounds good to me.
> >> >
> >> >>
> >> >> - timerfd_settime actions: this allows a single syscall to wait and
> >> >> adjust *both* monotonic and real-time wakeups.
> >> >
> >> > I'm not sure, doesn't this break orthogonality between epoll and timerfd?
> >>
> >> Yes. It's not very elegant, and more elegant ideas are welcome.
> >
> > What is the purpose of embedding timerfd operation here? Modifying timerfd
> > for each poll doesn't sound a common pattern to me.
>
> Setting a timeout is definitely a common pattern, hence this thread.
> But the current timeout interface sucks, and people should really use
> absolute time. (My epoll software uses absolute time.) But then
> users need to decide whether to have their timeout based on the
> monotonic clock or the realtime clock (or something else entirely).
> Some bigger programs may want both -- they may have internal events
> queued for certain times and for certain timeouts, and those should
> use realtime and monotonic respectively. Heck, users may also want
> separate slack values on those.
>
> Timerfd is the only thing we have right now that is anywhere near
> flexible enough. Obviously if epoll became fancy enough, then we
> could do away with the timerfd entirely here.
>
> >
> >>
> >> >
> >> >>
> >> >> Would this make sense? It could look like:
> >> >>
> >> >> int epoll_mod_and_pwait(int epfd,
> >> >> struct epoll_event *events, int maxevents,
> >> >> struct epoll_command *commands, int ncommands,
> >> >> const sigset_t *sigmask);
> >> >
> >> > What about flags?
> >> >
> >>
> >> No room. Maybe it should just be a struct for everything instead of
> >> separate args.
> >
> > Also no room for timeout. A single struct sounds the only way to go.
>
> That's what timerfd is for. I think it would be a bit weird to
> support "timeout" and detailed timerfd control.
I see what you mean. Thanks.
I still don't like hooking timerfd in the interface. Besides the unclean
interface, it also feels cubersome and overkill to let users setup and add a
dedicated timerfd to implement timeout.
How about this:
int epoll_mod_wait(int epfd, struct epoll_mod_wait_data *data);
struct epoll_mod_wait_data {
struct epoll_event *events;
int maxevents;
struct epoll_mod_cmd {
int op,
int fd;
void *data;
} *cmds;
int ncmds;
int flags;
sigset_t *sigmask;
};
Commands ops are:
EPOLL_CTL_ADD
@fd is the fd to modify; @data is epoll_event.
EPOLL_CTL_MOD
@fd is the fd to modify; @data is epoll_event.
EPOLL_CTL_DEL
@fd is the fd to modify; @data is epoll_event.
EPOLL_CTL_SET_TIMEOUT
@fd is ignored, @data is timespec.
Clock type and relative/absolute are selected by flags as below.
Flags are given to override timeout defaults:
EPOLL_FL_MONOTONIC_CLOCK
If set, don't use realtime clock, use monotonic clock.
EPOLL_FL_ABSOLUTE_TIMEOUT
If set, don't use relative timeout, use absolute timeout.
Thanks,
Fam
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