Re: [PATCH v1] Use CLOCK_MONOTONIC_RAW if available for get_clock().
Peter, Thanks for the quick response. I've informally socialized the issue and will update this thread when I get more information. That aside, I'd find using CLOCK_MONOTONIC_RAW valuable if, e.g., I wanted test an NTP daemon inside of a guest and didn't want the host providing an already-adjusted timebase. Would the behavior from my patch be more appropriate as a command-line option? v/r Joe On 9/30/21, 12:11 PM, "Peter Maydell" wrote: On Thu, 30 Sept 2021 at 17:04, Joe Tanen wrote: > > CLOCK_MONOTONIC_RAW provides an unadjusted system clock on some platforms, > which is closer in spirit to providing a guest with a raw hardware clock than > CLOCK_MONOTONIC. > > Using CLOCK_MONOTONIC_RAW also works around a current issue in OSX where > CLOCK_MONOTONIC has been observed to go backwards. > > Since CLOCK_MONOTONIC_RAW might not be available on all platforms, revert to > using CLOCK_MONOTONIC if it is not present. > > Signed-off-by: Joe Tanen I'm not sure we want to change behaviour everywhere to work around an OSX bug, though... Has this bug been reported to Apple ? Is there some kind of bug report ID or URL we can quote in the commit message ? -- PMM
Re: [PATCH v1] Use CLOCK_MONOTONIC_RAW if available for get_clock().
On Thu, 30 Sept 2021 at 17:04, Joe Tanen wrote: > > CLOCK_MONOTONIC_RAW provides an unadjusted system clock on some platforms, > which is closer in spirit to providing a guest with a raw hardware clock than > CLOCK_MONOTONIC. > > Using CLOCK_MONOTONIC_RAW also works around a current issue in OSX where > CLOCK_MONOTONIC has been observed to go backwards. > > Since CLOCK_MONOTONIC_RAW might not be available on all platforms, revert to > using CLOCK_MONOTONIC if it is not present. > > Signed-off-by: Joe Tanen I'm not sure we want to change behaviour everywhere to work around an OSX bug, though... Has this bug been reported to Apple ? Is there some kind of bug report ID or URL we can quote in the commit message ? -- PMM
[PATCH v1] Use CLOCK_MONOTONIC_RAW if available for get_clock().
CLOCK_MONOTONIC_RAW provides an unadjusted system clock on some platforms,
which is closer in spirit to providing a guest with a raw hardware clock than
CLOCK_MONOTONIC.
Using CLOCK_MONOTONIC_RAW also works around a current issue in OSX where
CLOCK_MONOTONIC has been observed to go backwards.
Since CLOCK_MONOTONIC_RAW might not be available on all platforms, revert to
using CLOCK_MONOTONIC if it is not present.
Signed-off-by: Joe Tanen
---
include/qemu/timer.h | 3 ++-
util/qemu-timer-common.c | 11 +++
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/include/qemu/timer.h b/include/qemu/timer.h
index 88ef114689..fb8f5074df 100644
--- a/include/qemu/timer.h
+++ b/include/qemu/timer.h
@@ -828,12 +828,13 @@ static inline int64_t get_clock(void)
#else
extern int use_rt_clock;
+extern clockid_t rt_clock;
static inline int64_t get_clock(void)
{
if (use_rt_clock) {
struct timespec ts;
-clock_gettime(CLOCK_MONOTONIC, );
+clock_gettime(rt_clock, );
return ts.tv_sec * 10LL + ts.tv_nsec;
} else {
/* XXX: using gettimeofday leads to problems if the date
diff --git a/util/qemu-timer-common.c b/util/qemu-timer-common.c
index cc1326f726..5039c5406c 100644
--- a/util/qemu-timer-common.c
+++ b/util/qemu-timer-common.c
@@ -49,13 +49,24 @@ static void __attribute__((constructor))
init_get_clock(void)
#else
int use_rt_clock;
+clockid_t rt_clock;
static void __attribute__((constructor)) init_get_clock(void)
{
struct timespec ts;
use_rt_clock = 0;
+#if (defined(__APPLE__) || defined(__linux__)) && defined(CLOCK_MONOTONIC_RAW)
+/* CLOCK_MONOTONIC_RAW is not available on all platforms or with all
+ * compiler flags.
+ */
+if (clock_gettime(CLOCK_MONOTONIC_RAW, ) == 0) {
+rt_clock = CLOCK_MONOTONIC_RAW;
+use_rt_clock = 1;
+} else
+#endif
if (clock_gettime(CLOCK_MONOTONIC, ) == 0) {
+rt_clock = CLOCK_MONOTONIC;
use_rt_clock = 1;
}
clock_start = get_clock();
--
2.31.1
