From: Thomas Gleixner Date: Sat, 19 Nov 2016 13:47:41 +0000 (+0000) Subject: x86/tsc: Prepare warp test for TSC adjustment X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=76d3b85158509cafec5be7675a97ef80118e288e;p=linux-beck.git 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 Reviewed-by: Ingo Molnar Cc: Peter Zijlstra Cc: Yinghai Lu Cc: Borislav Petkov Link: http://lkml.kernel.org/r/20161119134017.970859287@linutronix.de Signed-off-by: Thomas Gleixner --- diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 8f394eeb936e..9ad074c87e72 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; } /*