Commit-ID: eee6946e44510b61c35cf754f5505537c7a8eb77 Gitweb: http://git.kernel.org/tip/eee6946e44510b61c35cf754f5505537c7a8eb77 Author: Andy Lutomirski <[email protected]> AuthorDate: Thu, 25 Jun 2015 18:44:09 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Mon, 6 Jul 2015 15:23:29 +0200
x86/asm/tsc/sync: Use rdtsc_ordered() in check_tsc_warp() and drop extra barriers 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 <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Huang Rui <[email protected]> Cc: John Stultz <[email protected]> Cc: Len Brown <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Ralf Baechle <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: kvm ML <[email protected]> Link: http://lkml.kernel.org/r/387c4c3a75f875bcde6cd68cee013273a744f364.1434501121.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/tsc_sync.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index dd8d079..78083bf 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
