On Wed, 20 Jun 2018, Pavel Tatashin wrote:
> If architecture does not support exact boot time, it is challenging to
> estimate boot time without having a reference to the current persistent
> clock value. Yet, we cannot read the persistent clock time again, because
> this may lead to math discrepancies with the caller of read_boot_clock64()
> who have read the persistent clock at a different time.
>
> This is why it is better to provide two values simultaneously: the
> persistent clock value, and the boot time.
>
> Thus, we replace read_boot_clock64() with:
> read_persistent_wall_and_boot_offset(wall_time, boot_offset)
>
> Where wall_time is returned by read_persistent_clock()
> And boot_offset is wall_time - boot time
>
> We calculate boot_offset using the current value of local_clock() so
> architectures, that do not have a dedicated boot_clock but have early
> sched_clock(), such as SPARCv9, x86, and possibly more will benefit from
> this change by getting a better and more consistent estimate of the boot
> time without need for an arch specific implementation.
>
> Signed-off-by: Pavel Tatashin <pasha.tatas...@oracle.com>
> ---
> arch/arm/kernel/time.c | 12 +-------
> arch/s390/kernel/time.c | 11 +++++--
> include/linux/timekeeping.h | 3 +-
> kernel/time/timekeeping.c | 61 +++++++++++++++++++------------------
Please don't make that a wholesale patch. I surely indicated the steps
which are required and the steps can be done as separate patches easily,
Thanks,
tglx
