[CFR] Kevent timer improvements

[Konstantin Belousov]

On Sun, Apr 13, 2014 at 03:15:51PM +0200, Baptiste Daroussin wrote:
> I have splitted my patch in multiple parts, let start with the first one:
> adding NOTE_NSECONDS, NOTE_USECONDS, NOTE_NSECONDS
> 
> http://people.freebsd.org/~bapt/kevent_timer.diff

> Index: sys/kern/kern_event.c
> ===================================================================
> --- sys/kern/kern_event.c	(revision 264413)
> +++ sys/kern/kern_event.c	(working copy)
> @@ -524,14 +524,24 @@
>   * interval timer support code.
>   */
>  static __inline sbintime_t
> -timer2sbintime(intptr_t data)
> +timer2sbintime(intptr_t data, int flags)
>  {
> +	sbintime_t modifier;
>  
> +	modifier = SBT_1MS;
> +
> +	if (flags & NOTE_SECONDS)
> +		modifier = SBT_1S;
> +	else if (flags & NOTE_USECONDS)
> +		modifier = SBT_1US;
> +	else if (flags & NOTE_NSECONDS)
> +		modifier = SBT_1NS;
It is better to put the 'modifier = SBT_1MS;' statement as the else part.

That said, IMO it would be sometimes beneficial to have real flag to
specify milliseconds precision, in addition to milliseconds be the
default.
> +
>  #ifdef __LP64__
> -	if (data > SBT_MAX / SBT_1MS)
> +	if (data > SBT_MAX / modifier)
>  		return (SBT_MAX);
>  #endif
> -	return (SBT_1MS * data);
> +	return (modifier * data);
>  }
>  
>  static void
> @@ -547,7 +557,7 @@
>  	if ((kn->kn_flags & EV_ONESHOT) != EV_ONESHOT) {
>  		calloutp = (struct callout *)kn->kn_hook;
>  		callout_reset_sbt_on(calloutp,
> -		    timer2sbintime(kn->kn_sdata), 0 /* 1ms? */,
> +		    timer2sbintime(kn->kn_sdata, kn->kn_sfflags), 0 /* 1ms? */,
There, at least the comment about precision should be updated.
But, it seems that for the seconds precision, it makes sense to
specify e.g. 1/2 sec as precision; or add an API flag to allow imprecise
callout scheduling.

>  		    filt_timerexpire, kn, PCPU_GET(cpuid), 0);
>  	}
>  }
> @@ -566,7 +576,7 @@
>  		return (EINVAL);
>  	if ((intptr_t)kn->kn_sdata == 0 && (kn->kn_flags & EV_ONESHOT) == 0)
>  		kn->kn_sdata = 1;
> -	to = timer2sbintime(kn->kn_sdata);
> +	to = timer2sbintime(kn->kn_sdata, kn->kn_sfflags);
>  	if (to < 0)
>  		return (EINVAL);
>  
> Index: sys/sys/event.h
> ===================================================================
> --- sys/sys/event.h	(revision 264413)
> +++ sys/sys/event.h	(working copy)
> @@ -133,6 +133,11 @@
>  #define	NOTE_TRACKERR	0x00000002		/* could not track child */
>  #define	NOTE_CHILD	0x00000004		/* am a child process */
>  
> +/* additional flags for EVFILE_TIMER */
> +#define NOTE_SECONDS	0x00000001		/* data is seconds */
> +#define NOTE_USECONDS	0x00000002		/* data is microseconds */
> +#define NOTE_NSECONDS	0x00000004		/* data is nanoseconds */
> +
>  struct knote;
>  SLIST_HEAD(klist, knote);
>  struct kqueue;
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