On Mon, Jul 21, 2014 at 3:11 PM, Thomas Gleixner <t...@linutronix.de> wrote: > On Tue, 22 Jul 2014, Thomas Gleixner wrote: >> On Mon, 21 Jul 2014, Andy Lutomirski wrote: >> > On Mon, Jul 21, 2014 at 2:52 PM, Borislav Petkov <b...@alien8.de> wrote: >> > > On Mon, Jul 21, 2014 at 02:41:50PM -0700, Andy Lutomirski wrote: >> > >> How will this be compatible with the vdso? >> > > >> > > I've never thought about it yet. How compatible would you want it to be >> > > and what do you expect from it? >> > >> > I expect that users of __vdso_clock_gettime (e.g. glibc) will get the >> > correct time :) They use vread_tsc, and they can't use >> > preempt_disable, because they're in userspace. They also can't >> > directly access per-cpu variables. >> > >> > Turning off vdso tsc support on these machines would be an option. >> >> Correct. >> >> So if we make the TSC usable that way we need to mark it unusable for >> the VDSO and force vdso_*gettime* into the kernel. That will be way >> better than forcing the whole machine onto HPET. >> >> And once we are using the real syscall, the whole thing just works ... > > So all it needs is to do > > clocksource_tsc.archdata.vclock_mode = VCLOCK_NONE; > > if we do the magic per cpu offset trick to make the fcked up TSC > usable.
Just make sure this happens every time the tsc clocksource is selected -- it's possible to go back and forth. > > Thanks, > > tglx > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
