On Tue, 23 Feb 2021 23:11:43 +0800 Eric Gao <[email protected]> wrote:
> sometimes, we need the msgsnd or msgrcv syscall can return after a limited
> time, so that the business thread do not be blocked here all the time. In
> this case, I add the msgsnd_timed and msgrcv_timed syscall that with time
> parameter, which has a unit of ms.
Please cc Manfred and Davidlohr on ipc/ changes.
The above is a very brief description for a new syscall! Please go to
great lengths to tell us why this is considered useful - what are the
use cases?
Also, please fully describe the proposed syscall interface right here
in the changelog. Please be prepared to later prepare a full manpage.
> ...
> +SYSCALL_DEFINE5(msgsnd_timed, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
> + int, msgflg, long, timeoutms)
Specifying the timeout in milliseconds is problematic - it's very
coarse. See sys_epoll_pwait2()'s use of timespecs.
Hi Eric,
On 3/4/21 2:12 AM, Andrew Morton wrote:
> On Tue, 23 Feb 2021 23:11:43 +0800 Eric Gao <[email protected]> wrote:
>
>> sometimes, we need the msgsnd or msgrcv syscall can return after a limited
>> time, so that the business thread do not be blocked here all the time. In
>> this case, I add the msgsnd_timed and msgrcv_timed syscall that with time
>> parameter, which has a unit of ms.
> Please cc Manfred and Davidlohr on ipc/ changes.
>
> The above is a very brief description for a new syscall! Please go to
> great lengths to tell us why this is considered useful - what are the
> use cases?
>
> Also, please fully describe the proposed syscall interface right here
> in the changelog. Please be prepared to later prepare a full manpage.
>
>> ...
>> +SYSCALL_DEFINE5(msgsnd_timed, int, msqid, struct msgbuf __user *, msgp, size_t, msgsz,
>> + int, msgflg, long, timeoutms)
> Specifying the timeout in milliseconds is problematic - it's very
> coarse. See sys_epoll_pwait2()'s use of timespecs.
What about using an absolute timeout, like in mq_timedsend()?
That makes restart handling after signals far simpler.
> > - schedule();
> > +
> > + /* sometimes, we need msgsnd syscall return after a given time */
> > + if (timeoutms <= 0) {
> > + schedule();
> > + } else {
> > + timeoutms = schedule_timeout(timeoutms);
> > + if (timeoutms == 0)
> > + timeoutflag = true;
> > + }
>
> I wonder if this should be schedule_timeout_interruptible() or at least
> schedule_timeout_killable() instead of schedule_timeout(). If it should,
> this should probably be done as a separate change.
No. schedule_timeout_interruptible() just means that
__set_current_state() is called before the schedule_timeout().
The __set_current_state() is done directly in msg.c, before dropping the
lock.
--
Manfred