monotonic_clock() in arch/x86/time.c is more complex than needed: it
has basically two nested loops making sure the time data obtained from
Xen are valid.
Simplify that by merging some of the used sub-functions into the main
function and using only a single loop. Further simplify the code by
using struct vcpu_time_info for the local instance instead of defining
a similar structure in the code.
Signed-off-by: Juergen Gross <jgross@suse.com>
---
arch/x86/time.c | 58 ++++++++++++++-----------------------------------
1 file changed, 16 insertions(+), 42 deletions(-)
diff --git a/arch/x86/time.c b/arch/x86/time.c
index 7fd7abef..52916e15 100644
--- a/arch/x86/time.c
+++ b/arch/x86/time.c
@@ -44,24 +44,10 @@
*************************************************************************/
/* These are peridically updated in shared_info, and then copied here. */
-struct shadow_time_info {
- uint64_t tsc_timestamp; /* TSC at last update of time vals. */
- uint64_t system_timestamp; /* Time, in nanosecs, since boot. */
- uint32_t tsc_to_nsec_mul;
- int tsc_shift;
- uint32_t version;
-};
static struct timespec shadow_ts;
static uint32_t shadow_ts_version;
-static struct shadow_time_info shadow;
-
-static inline int time_values_up_to_date(void)
-{
- struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time;
-
- return shadow.version == src->version;
-}
+static struct vcpu_time_info shadow;
static inline int wc_values_up_to_date(void)
{
@@ -113,22 +99,7 @@ static unsigned long get_nsec_offset(void)
rdtscll(now);
delta = now - shadow.tsc_timestamp;
- return scale_delta(delta, shadow.tsc_to_nsec_mul, shadow.tsc_shift);
-}
-
-static void get_time_values_from_xen(void)
-{
- struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time;
-
- do {
- shadow.version = src->version;
- rmb();
- shadow.tsc_timestamp = src->tsc_timestamp;
- shadow.system_timestamp = src->system_time;
- shadow.tsc_to_nsec_mul = src->tsc_to_system_mul;
- shadow.tsc_shift = src->tsc_shift;
- rmb();
- } while ( (src->version & 1) | (shadow.version ^ src->version) );
+ return scale_delta(delta, shadow.tsc_to_system_mul, shadow.tsc_shift);
}
/*
@@ -138,19 +109,22 @@ static void get_time_values_from_xen(void)
*/
uint64_t monotonic_clock(void)
{
- uint64_t time;
- uint32_t local_time_version;
+ struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time;
- do {
- local_time_version = shadow.version;
- rmb();
- time = shadow.system_timestamp + get_nsec_offset();
- if ( !time_values_up_to_date() )
- get_time_values_from_xen();
- rmb();
- } while ( local_time_version != shadow.version );
+ if ( shadow.version != src->version )
+ {
+ do {
+ shadow.version = src->version;
+ rmb();
+ shadow.tsc_timestamp = src->tsc_timestamp;
+ shadow.system_time = src->system_time;
+ shadow.tsc_to_system_mul = src->tsc_to_system_mul;
+ shadow.tsc_shift = src->tsc_shift;
+ rmb();
+ } while ( (src->version & 1) || (shadow.version != src->version) );
+ }
- return time;
+ return shadow.system_time + get_nsec_offset();
}
static void update_wallclock(void)
--
2.43.0
Juergen Gross, le lun. 22 juil. 2024 14:16:43 +0200, a ecrit: > monotonic_clock() in arch/x86/time.c is more complex than needed: it > has basically two nested loops making sure the time data obtained from > Xen are valid. > > Simplify that by merging some of the used sub-functions into the main > function and using only a single loop. Further simplify the code by > using struct vcpu_time_info for the local instance instead of defining > a similar structure in the code. > > Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org> > --- > arch/x86/time.c | 58 ++++++++++++++----------------------------------- > 1 file changed, 16 insertions(+), 42 deletions(-) > > diff --git a/arch/x86/time.c b/arch/x86/time.c > index 7fd7abef..52916e15 100644 > --- a/arch/x86/time.c > +++ b/arch/x86/time.c > @@ -44,24 +44,10 @@ > *************************************************************************/ > > /* These are peridically updated in shared_info, and then copied here. */ > -struct shadow_time_info { > - uint64_t tsc_timestamp; /* TSC at last update of time vals. */ > - uint64_t system_timestamp; /* Time, in nanosecs, since boot. */ > - uint32_t tsc_to_nsec_mul; > - int tsc_shift; > - uint32_t version; > -}; > static struct timespec shadow_ts; > static uint32_t shadow_ts_version; > > -static struct shadow_time_info shadow; > - > -static inline int time_values_up_to_date(void) > -{ > - struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time; > - > - return shadow.version == src->version; > -} > +static struct vcpu_time_info shadow; > > static inline int wc_values_up_to_date(void) > { > @@ -113,22 +99,7 @@ static unsigned long get_nsec_offset(void) > rdtscll(now); > delta = now - shadow.tsc_timestamp; > > - return scale_delta(delta, shadow.tsc_to_nsec_mul, shadow.tsc_shift); > -} > - > -static void get_time_values_from_xen(void) > -{ > - struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time; > - > - do { > - shadow.version = src->version; > - rmb(); > - shadow.tsc_timestamp = src->tsc_timestamp; > - shadow.system_timestamp = src->system_time; > - shadow.tsc_to_nsec_mul = src->tsc_to_system_mul; > - shadow.tsc_shift = src->tsc_shift; > - rmb(); > - } while ( (src->version & 1) | (shadow.version ^ src->version) ); > + return scale_delta(delta, shadow.tsc_to_system_mul, shadow.tsc_shift); > } > > /* > @@ -138,19 +109,22 @@ static void get_time_values_from_xen(void) > */ > uint64_t monotonic_clock(void) > { > - uint64_t time; > - uint32_t local_time_version; > + struct vcpu_time_info *src = &HYPERVISOR_shared_info->vcpu_info[0].time; > > - do { > - local_time_version = shadow.version; > - rmb(); > - time = shadow.system_timestamp + get_nsec_offset(); > - if ( !time_values_up_to_date() ) > - get_time_values_from_xen(); > - rmb(); > - } while ( local_time_version != shadow.version ); > + if ( shadow.version != src->version ) > + { > + do { > + shadow.version = src->version; > + rmb(); > + shadow.tsc_timestamp = src->tsc_timestamp; > + shadow.system_time = src->system_time; > + shadow.tsc_to_system_mul = src->tsc_to_system_mul; > + shadow.tsc_shift = src->tsc_shift; > + rmb(); > + } while ( (src->version & 1) || (shadow.version != src->version) ); > + } > > - return time; > + return shadow.system_time + get_nsec_offset(); > } > > static void update_wallclock(void) > -- > 2.43.0 > -- Samuel "I don't know why, but first C programs tend to look a lot worse than first programs in any other language (maybe except for fortran, but then I suspect all fortran programs look like `firsts')" (By Olaf Kirch)
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