From: Thomas Gleixner Date: Thu, 9 Feb 2017 15:08:41 +0000 (+0100) Subject: x86/tsc: Avoid the large time jump when sanitizing TSC ADJUST X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f2e04214ef7f7e49d1e06109ad1b2718155dab25;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git x86/tsc: Avoid the large time jump when sanitizing TSC ADJUST Olof reported that on a machine which has a BIOS wreckaged TSC the timestamps in dmesg are making a large jump because the TSC value is jumping forward after resetting the TSC ADJUST register to a sane value. This can be avoided by calling the TSC ADJUST saniziting function before initializing the per cpu sched clock machinery. That takes the offset into account and avoid the time jump. What cannot be avoided is that the 'Firmware Bug' warnings on the secondary CPUs are printed with the large time offsets because it would be too much effort and ugly hackery to print those warnings into a buffer and emit them after the adjustemt on the starting CPUs. It's a firmware bug and should be fixed in firmware. The weird timestamps are collateral damage and just illustrate the sillyness of the BIOS folks: [ 0.397445] smp: Bringing up secondary CPUs ... [ 0.402100] x86: Booting SMP configuration: [ 0.406343] .... node #0, CPUs: #1 [1265776479.930667] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2978888639075328 CPU1: -2978888639183101 [1265776479.944664] TSC ADJUST synchronize: Reference CPU0: 0 CPU1: -2978888639183101 [ 0.508119] #2 [1265776480.032346] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2978888639075328 CPU2: -2978888639183677 [1265776480.044192] TSC ADJUST synchronize: Reference CPU0: 0 CPU2: -2978888639183677 [ 0.607643] #3 [1265776480.131874] [Firmware Bug]: TSC ADJUST differs: Reference CPU0: -2978888639075328 CPU3: -2978888639184530 [1265776480.143720] TSC ADJUST synchronize: Reference CPU0: 0 CPU3: -2978888639184530 [ 0.707108] smp: Brought up 1 node, 4 CPUs [ 0.711271] smpboot: Total of 4 processors activated (21698.88 BogoMIPS) Reported-by: Olof Johansson Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20170209151231.411460506@linutronix.de Signed-off-by: Thomas Gleixner --- diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index e41af597aed8..37e7cf544e51 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1356,6 +1356,9 @@ void __init tsc_init(void) (unsigned long)cpu_khz / 1000, (unsigned long)cpu_khz % 1000); + /* Sanitize TSC ADJUST before cyc2ns gets initialized */ + tsc_store_and_check_tsc_adjust(true); + /* * Secondary CPUs do not run through tsc_init(), so set up * all the scale factors for all CPUs, assuming the same @@ -1386,8 +1389,6 @@ void __init tsc_init(void) if (unsynchronized_tsc()) mark_tsc_unstable("TSCs unsynchronized"); - else - tsc_store_and_check_tsc_adjust(true); check_system_tsc_reliable();