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| author | Peter Zijlstra <peterz@infradead.org> | 2026-02-24 19:36:01 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-02-27 18:40:06 +0300 |
| commit | b7dd64778aa3f89de9afa1e81171cfe110ddc525 (patch) | |
| tree | 375c1b79b73330fb22205022be0b0a57b66bbd81 /include/linux/hrtimer.h | |
| parent | c8cdb9b516407a0b8c653c9c1d6f0931c3864384 (diff) | |
| download | linux-b7dd64778aa3f89de9afa1e81171cfe110ddc525.tar.xz | |
hrtimer: Provide LAZY_REARM mode
The hrtick timer is frequently rearmed before expiry and most of the time
the new expiry is past the armed one. As this happens on every context
switch it becomes expensive with scheduling heavy work loads especially in
virtual machines as the "hardware" reprogamming implies a VM exit.
Add a lazy rearm mode flag which skips the reprogamming if:
1) The timer was the first expiring timer before the rearm
2) The new expiry time is farther out than the armed time
This avoids a massive amount of reprogramming operations of the hrtick
timer for the price of eventually taking the alredy armed interrupt for
nothing.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163429.408524456@kernel.org
Diffstat (limited to 'include/linux/hrtimer.h')
| -rw-r--r-- | include/linux/hrtimer.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index b5003856fd60..c924bb2498db 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -31,6 +31,13 @@ * soft irq context * HRTIMER_MODE_HARD - Timer callback function will be executed in * hard irq context even on PREEMPT_RT. + * HRTIMER_MODE_LAZY_REARM - Avoid reprogramming if the timer was the + * first expiring timer and is moved into the + * future. Special mode for the HRTICK timer to + * avoid extensive reprogramming of the hardware, + * which is expensive in virtual machines. Risks + * a pointless expiry, but that's better than + * reprogramming on every context switch, */ enum hrtimer_mode { HRTIMER_MODE_ABS = 0x00, @@ -38,6 +45,7 @@ enum hrtimer_mode { HRTIMER_MODE_PINNED = 0x02, HRTIMER_MODE_SOFT = 0x04, HRTIMER_MODE_HARD = 0x08, + HRTIMER_MODE_LAZY_REARM = 0x10, HRTIMER_MODE_ABS_PINNED = HRTIMER_MODE_ABS | HRTIMER_MODE_PINNED, HRTIMER_MODE_REL_PINNED = HRTIMER_MODE_REL | HRTIMER_MODE_PINNED, |