search for: d8bb6f4c1670

On Tue, 18 Sep 2018, Thomas Gleixner wrote: > On Tue, 18 Sep 2018, Peter Zijlstra wrote: > > > Your memory serves you right. That's indeed observable on CPUs which > > > lack TSC_ADJUST. > > > > But, if the gtod code can observe this, then why doesn't the code that > > checks the sync? > > Because it depends where the involved CPUs are in the

On Tue, 18 Sep 2018, Thomas Gleixner wrote: > On Tue, 18 Sep 2018, Peter Zijlstra wrote: > > > Your memory serves you right. That's indeed observable on CPUs which > > > lack TSC_ADJUST. > > > > But, if the gtod code can observe this, then why doesn't the code that > > checks the sync? > > Because it depends where the involved CPUs are in the

...ust fail to see the havoc. > > Even with TSC adjust the TSC can be slightly off by design on multi-socket > systems. Here are the gory details: https://lore.kernel.org/lkml/3c1737210708230408i7a8049a9m5db49e6c4d89ab62 at mail.gmail.com/ The changelog has an explanation as well. d8bb6f4c1670 ("x86: tsc prevent time going backwards") I still have one of the machines which is affected by this. Thanks, tglx

...th TSC adjust the TSC can be slightly off by design on multi-socket > > systems. > > Here are the gory details: > > https://lore.kernel.org/lkml/3c1737210708230408i7a8049a9m5db49e6c4d89ab62 at mail.gmail.com/ > > The changelog has an explanation as well. > > d8bb6f4c1670 ("x86: tsc prevent time going backwards") > > I still have one of the machines which is affected by this. Are we sure this isn't a load vs rdtsc reorder? Because if I look at the current code: notrace static u64 vread_tsc(void) { u64 ret = (u64)rdtsc_ordered(); u64 last = g...

...th TSC adjust the TSC can be slightly off by design on multi-socket > > systems. > > Here are the gory details: > > https://lore.kernel.org/lkml/3c1737210708230408i7a8049a9m5db49e6c4d89ab62 at mail.gmail.com/ > > The changelog has an explanation as well. > > d8bb6f4c1670 ("x86: tsc prevent time going backwards") > > I still have one of the machines which is affected by this. Are we sure this isn't a load vs rdtsc reorder? Because if I look at the current code: notrace static u64 vread_tsc(void) { u64 ret = (u64)rdtsc_ordered(); u64 last = g...