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Fix a severe slowdown regression in the timer vDSO code related

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to the while() loop in __iter_div_u64_rem(), when the AUX-clock
 is enabled.
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'timers-urgent-2025-09-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fix from Ingo Molnar:
 "Fix a severe slowdown regression in the timer vDSO code related to the
  while() loop in __iter_div_u64_rem(), when the AUX-clock is enabled"

* tag 'timers-urgent-2025-09-07' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  vdso/vsyscall: Avoid slow division loop in auxiliary clock update
This commit is contained in:
Linus Torvalds 2025-09-07 08:29:44 -07:00
commit 6ab41fca2e
3 changed files with 18 additions and 5 deletions
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9
include/linux/timekeeper_internal.h
View File

@ -76,6 +76,7 @@ struct tk_read_base {
* @cs_was_changed_seq: The sequence number of clocksource change events
* @clock_valid: Indicator for valid clock
* @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset
* @monotonic_to_aux: CLOCK_MONOTONIC to CLOCK_AUX offset
* @cycle_interval: Number of clock cycles in one NTP interval
* @xtime_interval: Number of clock shifted nano seconds in one NTP
* interval.
@ -117,6 +118,9 @@ struct tk_read_base {
* @offs_aux is used by the auxiliary timekeepers which do not utilize any
* of the regular timekeeper offset fields.
*
* @monotonic_to_aux is a timespec64 representation of @offs_aux to
* accelerate the VDSO update for CLOCK_AUX.
*
* The cacheline ordering of the structure is optimized for in kernel usage of
* the ktime_get() and ktime_get_ts64() family of time accessors. Struct
* timekeeper is prepended in the core timekeeping code with a sequence count,
@ -159,7 +163,10 @@ struct timekeeper {
u8 cs_was_changed_seq;
u8 clock_valid;
struct timespec64 monotonic_to_boot;
union {
struct timespec64 monotonic_to_boot;
struct timespec64 monotonic_to_aux;
};
u64 cycle_interval;
u64 xtime_interval;

10
kernel/time/timekeeping.c
View File

@ -83,6 +83,12 @@ static inline bool tk_is_aux(const struct timekeeper *tk)
}
#endif
static inline void tk_update_aux_offs(struct timekeeper *tk, ktime_t offs)
{
tk->offs_aux = offs;
tk->monotonic_to_aux = ktime_to_timespec64(offs);
}
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@ -1506,7 +1512,7 @@ static int __timekeeping_inject_offset(struct tk_data *tkd, const struct timespe
timekeeping_restore_shadow(tkd);
return -EINVAL;
}
tks->offs_aux = offs;
tk_update_aux_offs(tks, offs);
}
timekeeping_update_from_shadow(tkd, TK_UPDATE_ALL);
@ -2937,7 +2943,7 @@ static int aux_clock_set(const clockid_t id, const struct timespec64 *tnew)
* xtime ("realtime") is not applicable for auxiliary clocks and
* kept in sync with "monotonic".
*/
aux_tks->offs_aux = ktime_sub(timespec64_to_ktime(*tnew), tnow);
tk_update_aux_offs(aux_tks, ktime_sub(timespec64_to_ktime(*tnew), tnow));
timekeeping_update_from_shadow(aux_tkd, TK_UPDATE_ALL);
return 0;

4
kernel/time/vsyscall.c
View File

@ -159,10 +159,10 @@ void vdso_time_update_aux(struct timekeeper *tk)
if (clock_mode != VDSO_CLOCKMODE_NONE) {
fill_clock_configuration(vc, &tk->tkr_mono);
vdso_ts->sec = tk->xtime_sec;
vdso_ts->sec = tk->xtime_sec + tk->monotonic_to_aux.tv_sec;
nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
nsec += tk->offs_aux;
nsec += tk->monotonic_to_aux.tv_nsec;
vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &nsec);
nsec = nsec << tk->tkr_mono.shift;
vdso_ts->nsec = nsec;