Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [PATCH v2 17/17] x86/tsc: In read_tsc, use rdtsc_ordered() instead of get_cycles() | Date | Fri, 12 Jun 2015 16:44:57 -0700 |
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There are two logical changes here. First, this removes a check for cpu_has_tsc. That check is unnecessary, as we don't register the TSC as a clocksource on systems that have no TSC. Second, it adds a barrier, thus preventing observable non-monotonicity.
I suspect that the missing barrier was never a problem in practice because system calls themselves were heavy enough barriers to prevent user code from observing time warps due to speculation. (Without the corresponding barrier in the vDSO, however, non-monotonicity is easy to detect.)
Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 5eb4d91ce9db..c3b6c04c5bf7 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -961,7 +961,7 @@ static struct clocksource clocksource_tsc; */ static cycle_t read_tsc(struct clocksource *cs) { - return (cycle_t)get_cycles(); + return (cycle_t)rdtsc_ordered(); } /* -- 2.4.2
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