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[PULL 14/35] hw/ppc: Round up the decrementer interval when converting t
From: |
Cédric Le Goater |
Subject: |
[PULL 14/35] hw/ppc: Round up the decrementer interval when converting to ns |
Date: |
Mon, 4 Sep 2023 11:06:09 +0200 |
From: Nicholas Piggin <npiggin@gmail.com>
The rule of timers is typically that they should never expire before the
timeout, but some time afterward. Rounding timer intervals up when doing
conversion is the right thing to do.
Under most circumstances it is impossible observe the decrementer
interrupt before the dec register has triggered. However with icount
timing, problems can arise. For example setting DEC to 0 can schedule
the timer for now, causing it to fire before any more instructions
have been executed and DEC is still 0.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
hw/ppc/ppc.c | 31 +++++++++++++++++++------------
1 file changed, 19 insertions(+), 12 deletions(-)
diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index 423a3a117ae2..13eb45f4b77e 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -482,14 +482,26 @@ void ppce500_set_mpic_proxy(bool enabled)
/*****************************************************************************/
/* PowerPC time base and decrementer emulation */
+/*
+ * Conversion between QEMU_CLOCK_VIRTUAL ns and timebase (TB) ticks:
+ * TB ticks are arrived at by multiplying tb_freq then dividing by
+ * ns per second, and rounding down. TB ticks drive all clocks and
+ * timers in the target machine.
+ *
+ * Converting TB intervals to ns for the purpose of setting a
+ * QEMU_CLOCK_VIRTUAL timer should go the other way, but rounding
+ * up. Rounding down could cause the timer to fire before the TB
+ * value has been reached.
+ */
static uint64_t ns_to_tb(uint32_t freq, int64_t clock)
{
return muldiv64(clock, freq, NANOSECONDS_PER_SECOND);
}
-static int64_t tb_to_ns(uint32_t freq, uint64_t tb)
+/* virtual clock in TB ticks, not adjusted by TB offset */
+static int64_t tb_to_ns_round_up(uint32_t freq, uint64_t tb)
{
- return muldiv64(tb, NANOSECONDS_PER_SECOND, freq);
+ return muldiv64_round_up(tb, NANOSECONDS_PER_SECOND, freq);
}
uint64_t cpu_ppc_get_tb(ppc_tb_t *tb_env, uint64_t vmclk, int64_t tb_offset)
@@ -847,7 +859,7 @@ static void __cpu_ppc_store_decr(PowerPCCPU *cpu, uint64_t
*nextp,
/* Calculate the next timer event */
now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
- next = now + tb_to_ns(tb_env->decr_freq, value);
+ next = now + tb_to_ns_round_up(tb_env->decr_freq, value);
*nextp = next;
/* Adjust timer */
@@ -1139,9 +1151,7 @@ static void cpu_4xx_fit_cb (void *opaque)
/* Cannot occur, but makes gcc happy */
return;
}
- next = now + tb_to_ns(tb_env->tb_freq, next);
- if (next == now)
- next++;
+ next = now + tb_to_ns_round_up(tb_env->tb_freq, next);
timer_mod(ppc40x_timer->fit_timer, next);
env->spr[SPR_40x_TSR] |= 1 << 26;
if ((env->spr[SPR_40x_TCR] >> 23) & 0x1) {
@@ -1167,11 +1177,10 @@ static void start_stop_pit (CPUPPCState *env, ppc_tb_t
*tb_env, int is_excp)
} else {
trace_ppc4xx_pit_start(ppc40x_timer->pit_reload);
now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
- next = now + tb_to_ns(tb_env->decr_freq, ppc40x_timer->pit_reload);
+ next = now + tb_to_ns_round_up(tb_env->decr_freq,
+ ppc40x_timer->pit_reload);
if (is_excp)
next += tb_env->decr_next - now;
- if (next == now)
- next++;
timer_mod(tb_env->decr_timer, next);
tb_env->decr_next = next;
}
@@ -1226,9 +1235,7 @@ static void cpu_4xx_wdt_cb (void *opaque)
/* Cannot occur, but makes gcc happy */
return;
}
- next = now + tb_to_ns(tb_env->decr_freq, next);
- if (next == now)
- next++;
+ next = now + tb_to_ns_round_up(tb_env->decr_freq, next);
trace_ppc4xx_wdt(env->spr[SPR_40x_TCR], env->spr[SPR_40x_TSR]);
switch ((env->spr[SPR_40x_TSR] >> 30) & 0x3) {
case 0x0:
--
2.41.0
- [PULL 01/35] target/ppc: Generate storage interrupts for radix RC changes, (continued)
- [PULL 01/35] target/ppc: Generate storage interrupts for radix RC changes, Cédric Le Goater, 2023/09/04
- [PULL 05/35] target/ppc: Suppress single step interrupts on rfi-type instructions, Cédric Le Goater, 2023/09/04
- [PULL 04/35] target/ppc: Improve book3s branch trace interrupt for v2.07S, Cédric Le Goater, 2023/09/04
- [PULL 07/35] target/ppc: Implement watchpoint debug facility for v2.07S, Cédric Le Goater, 2023/09/04
- [PULL 08/35] spapr: implement H_SET_MODE debug facilities, Cédric Le Goater, 2023/09/04
- [PULL 09/35] ppc/vhyp: reset exception state when handling vhyp hcall, Cédric Le Goater, 2023/09/04
- [PULL 10/35] ppc/vof: Fix missed fields in VOF cleanup, Cédric Le Goater, 2023/09/04
- [PULL 11/35] hw/ppc/ppc.c: Tidy over-long lines, Cédric Le Goater, 2023/09/04
- [PULL 12/35] hw/ppc: Introduce functions for conversion between timebase and nanoseconds, Cédric Le Goater, 2023/09/04
- [PULL 13/35] host-utils: Add muldiv64_round_up, Cédric Le Goater, 2023/09/04
- [PULL 14/35] hw/ppc: Round up the decrementer interval when converting to ns,
Cédric Le Goater <=
- [PULL 15/35] hw/ppc: Avoid decrementer rounding errors, Cédric Le Goater, 2023/09/04
- [PULL 16/35] target/ppc: Sign-extend large decrementer to 64-bits, Cédric Le Goater, 2023/09/04
- [PULL 17/35] hw/ppc: Always store the decrementer value, Cédric Le Goater, 2023/09/04
- [PULL 18/35] target/ppc: Migrate DECR SPR, Cédric Le Goater, 2023/09/04
- [PULL 19/35] hw/ppc: Reset timebase facilities on machine reset, Cédric Le Goater, 2023/09/04
- [PULL 20/35] hw/ppc: Read time only once to perform decrementer write, Cédric Le Goater, 2023/09/04
- [PULL 21/35] target/ppc: Fix CPU reservation migration for record-replay, Cédric Le Goater, 2023/09/04
- [PULL 23/35] spapr: Fix machine reset deadlock from replay-record, Cédric Le Goater, 2023/09/04
- [PULL 25/35] tests/avocado: boot ppc64 pseries replay-record test to Linux VFS mount, Cédric Le Goater, 2023/09/04
- [PULL 24/35] spapr: Fix record-replay machine reset consuming too many events, Cédric Le Goater, 2023/09/04