git: 0def80f1a5c8 - main - time(3): Align fast clock times to avoid firing multiple timers.

[Hans Petter Selasky]

The branch main has been updated by hselasky:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=0def80f1a5c8f7a02b92c823e5c71f9f746c3e6b

commit 0def80f1a5c8f7a02b92c823e5c71f9f746c3e6b
Author:     Hans Petter Selasky <hsela...@freebsd.org>
AuthorDate: 2022-10-03 08:54:40 +0000
Commit:     Hans Petter Selasky <hsela...@freebsd.org>
CommitDate: 2022-10-03 15:53:17 +0000

    time(3): Align fast clock times to avoid firing multiple timers.
    
    In non-periodic mode absolute timers fire at exactly the time given.
    When specifying a fast clock, align the firing time so that less
    timer interrupt events are needed.
    
    Reviewed by:    rrs @
    Differential Revision:  https://reviews.freebsd.org/D36858
    MFC after:      1 week
    Sponsored by:   NVIDIA Networking
---
 sys/kern/kern_umtx.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index 6b4e3ca38d03..75ce1dc43f81 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -706,6 +706,7 @@ umtx_abs_timeout_getsbt(struct umtx_abs_timeout *timo, 
sbintime_t *sbt,
 {
        struct bintime bt, bbt;
        struct timespec tts;
+       sbintime_t rem;
 
        switch (timo->clockid) {
 
@@ -738,14 +739,24 @@ umtx_abs_timeout_getsbt(struct umtx_abs_timeout *timo, 
sbintime_t *sbt,
                        return (0);
                }
                *sbt = bttosbt(bt);
+
+               /*
+                * Check if the absolute time should be aligned to
+                * avoid firing multiple timer events in non-periodic
+                * timer mode.
+                */
                switch (timo->clockid) {
                case CLOCK_REALTIME_FAST:
                case CLOCK_MONOTONIC_FAST:
                case CLOCK_UPTIME_FAST:
-                       *sbt += tc_tick_sbt;
+                       rem = *sbt % tc_tick_sbt;
+                       if (__predict_true(rem != 0))
+                               *sbt += tc_tick_sbt - rem;
                        break;
                case CLOCK_SECOND:
-                       *sbt += SBT_1S;
+                       rem = *sbt % SBT_1S;
+                       if (__predict_true(rem != 0))
+                               *sbt += SBT_1S - rem;
                        break;
                }
                *flags = C_ABSOLUTE;