PC unable to resume after suspend to ram. This patch make this regression for me: commit 47001d603375f857a7fab0e9c095d964a1ea0039 Author: Thomas Gleixner <tglx@linutronix.de> Date: Tue Apr 1 19:45:18 2008 +0200 x86: tsc prevent time going backwards We already catch most of the TSC problems by sanity checks, but there is a subtle bug which has been in the code for ever. This can cause time jumps in the range of hours. This was reported in: http://lkml.org/lkml/2007/8/23/96 and http://lkml.org/lkml/2008/3/31/23 I was able to reproduce the problem with a gettimeofday loop test on a dual core and a quad core machine which both have sychronized TSCs. The TSCs seems not to be perfectly in sync though, but the kernel is not able to detect the slight delta in the sync check. Still there exists an extremly small window where this delta can be observed with a real big time jump. So far I was only able to reproduce this with the vsyscall gettimeofday implementation, but in theory this might be observable with the syscall based version as well. CPU 0 updates the clock source variables under xtime/vyscall lock and CPU1, where the TSC is slighty behind CPU0, is reading the time right after the seqlock was unlocked. The clocksource reference data was updated with the TSC from CPU0 and the value which is read from TSC on CPU1 is less than the reference data. This results in a huge delta value due to the unsigned subtraction of the TSC value and the reference value. This algorithm can not be changed due to the support of wrapping clock sources like pm timer. The huge delta is converted to nanoseconds and added to xtime, which is then observable by the caller. The next gettimeofday call on CPU1 will show the correct time again as now the TSC has advanced above the reference value. To prevent this TSC specific wreckage we need to compare the TSC value against the reference value and return the latter when it is larger than the actual TSC value. I pondered to mark the TSC unstable when the readout is smaller than the reference value, but this would render an otherwise good and fast clocksource unusable without a real good reason. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
fixed by commit 5b13d863573e746739ccfc24ac1a9473cfee8df1
Created attachment 15686 [details] dmesg [ 2.128371] Magic number: 0:835:626 [ 2.128371] hash matches drivers/base/power/main.c:207 [ 2.128482] hash matches device 0000:00:1b.0
Created attachment 15687 [details] Test patch which presets the tsc->cycle_last value on resume Alexey, can you test the attached patch on top of Linus latest ? Thanks, tglx
This patch working for me. Thanks, Alex
> ------- Comment #4 from bug-track@fisher-privat.net 2008-04-09 02:28 ------- > This patch working for me. > Thanks, > Alex Alex, thanks for testing. I queue it for 2.6.26 Thanks, tglx