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3da02409af
As reported in the community forum [0][1], QEMU processes for Linux
guests would consume more CPU on the host after an update to QEMU 9.2.
The issue was reproduced and bisecting pointed to QEMU commit
f0ccf77078 ("hpet: fix and cleanup persistence of interrupt status").
Some quick experimentation suggests that in particular the last part
is responsible for the issue:
> - the timer must be kept running even if not enabled, in
> order to set the ISR flag, so writes to HPET_TN_CFG must
> not call hpet_del_timer()
Users confirmed that setting the hpet=off machine flag works around
the issue[0]. For Windows (7 or later) guests, the flag is already
disabled, because of issues in the past [2].
Upstream suggested reverting the relevant patches for now [3], because
other issues were reported too. All except commit 5895879aca ("hpet:
remove unnecessary variable "index"") are actually dependent on each
other for cleanly reverting f0ccf77078, and while not strictly
required, that one was reverted too for completeness.
[0]: https://forum.proxmox.com/threads/163694/
[1]: https://forum.proxmox.com/threads/161849/post-756793
[2]: https://lists.proxmox.com/pipermail/pve-devel/2012-December/004958.html
[3]: https://lore.kernel.org/qemu-devel/CABgObfaKJ5NFVKmYLFmu4C0iZZLJJtcWksLCzyA0tBoz0koZ4A@mail.gmail.com/
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
51 lines
1.8 KiB
Diff
51 lines
1.8 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Fiona Ebner <f.ebner@proxmox.com>
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Date: Wed, 19 Mar 2025 17:31:05 +0100
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Subject: [PATCH] Revert "hpet: avoid timer storms on periodic timers"
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This reverts commit 7c912ffb59e8137091894d767433e65c3df8b0bf.
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Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
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---
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hw/timer/hpet.c | 13 ++-----------
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1 file changed, 2 insertions(+), 11 deletions(-)
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diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
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index 5399f1b2a3..8ccc421cbb 100644
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--- a/hw/timer/hpet.c
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+++ b/hw/timer/hpet.c
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@@ -59,7 +59,6 @@ typedef struct HPETTimer { /* timers */
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uint8_t wrap_flag; /* timer pop will indicate wrap for one-shot 32-bit
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* mode. Next pop will be actual timer expiration.
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*/
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- uint64_t last; /* last value armed, to avoid timer storms */
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} HPETTimer;
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struct HPETState {
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@@ -267,7 +266,6 @@ static int hpet_post_load(void *opaque, int version_id)
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for (i = 0; i < s->num_timers; i++) {
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HPETTimer *t = &s->timer[i];
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t->cmp64 = hpet_calculate_cmp64(t, s->hpet_counter, t->cmp);
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- t->last = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - NANOSECONDS_PER_SECOND;
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}
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/* Recalculate the offset between the main counter and guest time */
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if (!s->hpet_offset_saved) {
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@@ -366,15 +364,8 @@ static const VMStateDescription vmstate_hpet = {
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static void hpet_arm(HPETTimer *t, uint64_t tick)
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{
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- uint64_t ns = hpet_get_ns(t->state, tick);
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-
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- /* Clamp period to reasonable min value (1 us) */
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- if (timer_is_periodic(t) && ns - t->last < 1000) {
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- ns = t->last + 1000;
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- }
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-
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- t->last = ns;
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- timer_mod(t->qemu_timer, ns);
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+ /* FIXME: Clamp period to reasonable min value? */
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+ timer_mod(t->qemu_timer, hpet_get_ns(t->state, tick));
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}
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/*
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