On 6/11/25 12:22 AM, Paolo Bonzini wrote:
Il mar 10 giu 2025, 23:28 Pierrick Bouvier <pierrick.bouv...@linaro.org
<mailto:pierrick.bouv...@linaro.org>> ha scritto:
This factor is applied to time spent since we read clock for the first
time. It impacts value returned by get_clock() and get_clock_realtime().
Sounds like a good idea, however it needs a couple changes:
1) different clocks have different starts, so the clock_start must be
stored per clock type
I was not sure if several clocks are used, so I'll simply use static in
concerned functions.
2) dilation must be applied to timers too.
From what I saw, timers either use clock function (already dilated), or
rely on cpu_get_host_ticks().
Do you suggest to dilate time returned by cpu_get_host_ticks(), or
something different?
As to the option, it's not immediately clear is <1 is a speed up or a
slow down. Maybe speed-factor=N is more clearly speeding up things if N>1?
+ g_assert(now >= clock_start);
You're right, it's not obvious.
I'm ok with speed-factor name.
The assertion is not needed, and can even fail in cases involving
daylight savings time; perhaps you can assert that the result is
positive instead?
+ if (!clock_time_dilation) {
+ return now;
+ }
Just initialize it to 1?
For exactly the same reason you mention under, possible loss of
precision. If my math is correct, we can only have a precision of 256
nanoseconds at this epoch time.
Adding an intermediate cast solves this though, so we can have a default
value of 1.
+ return clock_start + (now - clock_start) * clock_time_dilation;
Please cast back to integer after multiplying. Adding back clock_start
in floating point format loses precision (doubles have only 53 bits of
precision; seconds use 32 of them if the base is 1970, and nanoseconds
don't have the 30 bits they need).
I'll add the cast.
+}
+
/*
* Low level clock functions
*/
@@ -811,11 +823,9 @@ static inline int64_t get_clock_realtime(void)
struct timeval tv;
gettimeofday(&tv, NULL);
- return tv.tv_sec * 1000000000LL + (tv.tv_usec * 1000);
+ return dilate_time(tv.tv_sec * 1000000000LL + (tv.tv_usec * 1000));
}
-extern int64_t clock_start;
-
/* Warning: don't insert tracepoints into these functions, they are
also used by simpletrace backend and tracepoints would cause
an infinite recursion! */
@@ -826,7 +836,7 @@ static inline int64_t get_clock(void)
{
LARGE_INTEGER ti;
QueryPerformanceCounter(&ti);
- return muldiv64(ti.QuadPart, NANOSECONDS_PER_SECOND, clock_freq);
+ dilate_time(muldiv64(ti.QuadPart, NANOSECONDS_PER_SECOND,
clock_freq));
Missing "return".
Thanks, I caught this quickly after sending also.
Paolo
}
#else
@@ -838,10 +848,10 @@ static inline int64_t get_clock(void)
if (use_rt_clock) {
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
- return ts.tv_sec * 1000000000LL + ts.tv_nsec;
+ return dilate_time(ts.tv_sec * 1000000000LL + ts.tv_nsec);
} else {
/* XXX: using gettimeofday leads to problems if the date
- changes, so it should be avoided. */
+ changes, so it should be avoided. Time is already
dilated. */
return get_clock_realtime();
}
}
diff --git a/util/qemu-timer-common.c b/util/qemu-timer-common.c
index cc1326f7264..d8895aaccad 100644
--- a/util/qemu-timer-common.c
+++ b/util/qemu-timer-common.c
@@ -28,6 +28,7 @@
/* real time host monotonic timer */
int64_t clock_start;
+double clock_time_dilation;
#ifdef _WIN32
--
2.47.2
Thanks,
Pierrick
