Re: [PATCH v2 1/6] x86/time: calibrate TSC against platform timer

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 03/08/16 14:00, Jan Beulich wrote:
> ... instead of unconditionally against the PIT. This allows for local
> and master system times to remain in better sync (which matters even
> when, on any modern system, the master time is really used only during
> secondary CPU bringup, as the error between the two is in fact
> noticable in cross-CPU NOW() invocation monotonicity).
>
> This involves moving the init_platform_timer() invocation into
> early_time_init(), splitting out the few things which really need to be
> done in init_xen_time(). That in turn allows dropping the open coded
> PIT initialization from init_IRQ() (it was needed for APIC clock
> calibration, which runs between early_time_init() and init_xen_time()).
>
> In the course of this re-ordering also set the timer channel 2 gate low
> after having finished calibration. This should be benign to overall
> system operation, but appears to be the more clean state.
>
> Also do away with open coded 8254 register manipulation from 8259 code.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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