search for: get_kvmclock_n

...> host_tsc_clocksource = kvm_get_time_and_clockread( > &ka->master_kernel_ns, > &ka->master_cycle_now); > > kvm_get_time_and_clockread() gets those values from > do_monotonic_boot(), which, barring bugs, should cause > get_kvmclock_ns() to return exactly the same thing as > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > roundabout manner. > > So what am I missing? Is there actually something wrong with my patch? For the bug mentioned in the comment not to happen, you must only read TSC and add...

...> host_tsc_clocksource = kvm_get_time_and_clockread( > &ka->master_kernel_ns, > &ka->master_cycle_now); > > kvm_get_time_and_clockread() gets those values from > do_monotonic_boot(), which, barring bugs, should cause > get_kvmclock_ns() to return exactly the same thing as > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > roundabout manner. > > So what am I missing? Is there actually something wrong with my patch? For the bug mentioned in the comment not to happen, you must only read TSC and add...

...( > > > &ka->master_kernel_ns, > > > &ka->master_cycle_now); > > > > > > kvm_get_time_and_clockread() gets those values from > > > do_monotonic_boot(), which, barring bugs, should cause > > > get_kvmclock_ns() to return exactly the same thing as > > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > > roundabout manner. > > > > > > So what am I missing? Is there actually something wrong with my patch? > > > > For the bug mentioned in...

...( > > > &ka->master_kernel_ns, > > > &ka->master_cycle_now); > > > > > > kvm_get_time_and_clockread() gets those values from > > > do_monotonic_boot(), which, barring bugs, should cause > > > get_kvmclock_ns() to return exactly the same thing as > > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > > roundabout manner. > > > > > > So what am I missing? Is there actually something wrong with my patch? > > > > For the bug mentioned in...

...and using those two clocks to as a "base + offset". > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > updating the time offset. So can you explain how my patch is > > > incorrect? > > > > ktime_get_boot_ns() has frequency correction applied, while > > readi...

...and using those two clocks to as a "base + offset". > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > updating the time offset. So can you explain how my patch is > > > incorrect? > > > > ktime_get_boot_ns() has frequency correction applied, while > > readi...

...e = kvm_get_time_and_clockread( > > &ka->master_kernel_ns, > > &ka->master_cycle_now); > > > > kvm_get_time_and_clockread() gets those values from > > do_monotonic_boot(), which, barring bugs, should cause > > get_kvmclock_ns() to return exactly the same thing as > > ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather > > roundabout manner. > > > > So what am I missing? Is there actually something wrong with my patch? > > For the bug mentioned in the comment not to happen, yo...

On Thu, Oct 04, 2018 at 03:15:32PM -0700, Andy Lutomirski wrote: > For better or for worse, I'm trying to understand this code. So far, > I've come up with this patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/vdso-tglx&id=14fd71e12b1c4492a06f368f75041f263e6862bf > > Is it correct, or am I missing some subtlety? The master

On Thu, Oct 04, 2018 at 03:15:32PM -0700, Andy Lutomirski wrote: > For better or for worse, I'm trying to understand this code. So far, > I've come up with this patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/vdso-tglx&id=14fd71e12b1c4492a06f368f75041f263e6862bf > > Is it correct, or am I missing some subtlety? The master

...masterclock data is updated here: host_tsc_clocksource = kvm_get_time_and_clockread( &ka->master_kernel_ns, &ka->master_cycle_now); kvm_get_time_and_clockread() gets those values from do_monotonic_boot(), which, barring bugs, should cause get_kvmclock_ns() to return exactly the same thing as ktime_get_boot_ns() + ka->kvmclock_offset, albeit in a rather roundabout manner. So what am I missing? Is there actually something wrong with my patch? > > See the following comment on x86.c: I read that comment, and it's not obvious to me ho...

...d the other is TSC), > and using those two clocks to as a "base + offset". > > As the comment explains, if you do that, can't guarantee monotonicity. > > > actually calling ktime_get_boot_ns() could be non-monotonic > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > for VM timing as such -- it's used for the IOCTL interfaces for > > updating the time offset. So can you explain how my patch is > > incorrect? > > ktime_get_boot_ns() has frequency correction applied, while > reading masterclock + TSC offset do...

...ks to as a "base + offset". > > > > > > As the comment explains, if you do that, can't guarantee monotonicity. > > > > > > > actually calling ktime_get_boot_ns() could be non-monotonic > > > > with respect to the kvmclock timing. But get_kvmclock_ns() isn't used > > > > for VM timing as such -- it's used for the IOCTL interfaces for > > > > updating the time offset. So can you explain how my patch is > > > > incorrect? > > > > > > ktime_get_boot_ns() has frequency correction appli...