@@ -39,16 +39,15 @@ static cycles_t max_warp;
static int nr_warps;
/*
- * TSC-warp measurement loop running on both CPUs:
+ * TSC-warp measurement loop running on both CPUs. This is not called
+ * if there is no TSC.
*/
static void check_tsc_warp(unsigned int timeout)
{
cycles_t start, now, prev, end;
int i;
- rdtsc_barrier();
- start = get_cycles();
- rdtsc_barrier();
+ start = rdtsc_ordered();
/*
* The measurement runs for 'timeout' msecs:
*/
@@ -63,9 +62,7 @@ static void check_tsc_warp(unsigned int timeout)
*/
arch_spin_lock(&sync_lock);
prev = last_tsc;
- rdtsc_barrier();
- now = get_cycles();
- rdtsc_barrier();
+ now = rdtsc_ordered();
last_tsc = now;
arch_spin_unlock(&sync_lock);
@@ -126,7 +123,7 @@ void check_tsc_sync_source(int cpu)
/*
* No need to check if we already know that the TSC is not
- * synchronized:
+ * synchronized or if we have no TSC.
*/
if (unsynchronized_tsc())
return;
@@ -190,6 +187,7 @@ void check_tsc_sync_target(void)
{
int cpus = 2;
+ /* Also aborts if there is no TSC. */
if (unsynchronized_tsc() || tsc_clocksource_reliable)
return;
Using get_cycles was unnecessary: check_tsc_warp() is not called on TSC-less systems. Replace rdtsc_barrier(); get_cycles() with rdtsc_ordered(). While we're at it, make the somewhat more dangerous change of removing barrier_before_rdtsc after RDTSC in the TSC warp check code. This should be okay, though -- the vDSO TSC code doesn't have that barrier, so, if removing the barrier from the warp check would cause us to detect a warp that we otherwise wouldn't detect, then we have a genuine bug. Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/kernel/tsc_sync.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)