[PATCH 0/3] x86/platform/UV: Update TSC support

From: mike.travis
Date: Thu Sep 21 2017 - 16:22:37 EST



The UV BIOS goes to considerable effort to get the TSC synchronization
accurate across the entire system. Included in that are multiple
chassis that can have 32+ sockets. The architecture also supports an
external high resolution clock to help all the chassis and CPU's in
maintaining this synchronization.

As a result the UV system BIOS provides much better TSC accuracy than
the current kernel TSC ADJUST functions. This is extremely important in
applications that, for example, store and access data bases.

These two patches disable an assumption made by the kernel TSC ADJUST
functions that are not applicable to the UV system (and maybe others?).
That being that Socket 0 in the system should have a TSC ADJUST value
of zero. This is incorrect when all the chassis are started asynchronously
to each other, therefore which TSC's are farther advanced is not predictable.
The UV BIOS deals with this scenario correctly.

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