Commit-ID: 1e849cff359ccd8b6f3096205e3759e70f8d30ea Gitweb: http://git.kernel.org/tip/1e849cff359ccd8b6f3096205e3759e70f8d30ea Author: Thomas Gleixner <[email protected]> AuthorDate: Sat, 19 Nov 2016 13:47:41 +0000 Committer: Thomas Gleixner <[email protected]> CommitDate: Tue, 29 Nov 2016 17:29:48 +0100
x86/tsc: Prepare warp test for TSC adjustment To allow TSC compensation cross nodes its necessary to know in which direction the TSC warp was observed. Return the maximum observed value on the calling CPU so the caller can determine the direction later. Signed-off-by: Thomas Gleixner <[email protected]> Reviewed-by: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Yinghai Lu <[email protected]> Cc: Borislav Petkov <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Thomas Gleixner <[email protected]> --- arch/x86/kernel/tsc_sync.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 8642223..8a4ef7e 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -166,9 +166,9 @@ static int random_warps; * 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) +static cycles_t check_tsc_warp(unsigned int timeout) { - cycles_t start, now, prev, end; + cycles_t start, now, prev, end, cur_max_warp = 0; int i, cur_warps = 0; start = rdtsc_ordered(); @@ -209,6 +209,7 @@ static void check_tsc_warp(unsigned int timeout) if (unlikely(prev > now)) { arch_spin_lock(&sync_lock); max_warp = max(max_warp, prev - now); + cur_max_warp = max_warp; /* * Check whether this bounces back and forth. Only * one CPU should observe time going backwards. @@ -223,6 +224,7 @@ static void check_tsc_warp(unsigned int timeout) WARN(!(now-start), "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n", now-start, end-start); + return cur_max_warp; } /*
