Re: [PATCH 04/13] migration/postcopy: Make all blocktime vars 64bits

[Fabiano Rosas <farosas@suse.de>]

Peter Xu <peterx@redhat.com> writes:

> I am guessing it was used to be 32bits because of the atomic ops.  Now all
> the atomic ops are gone and we're protected by a mutex instead, it's ok we
> can switch to 64 bits.
>
> Reasons to move over:
>
>   - Allow further patches to change the unit from ms to us: with postcopy
>   preempt mode, we're really into hundreds of microseconds level on
>   blocktime.  We'd better be able to trap those.
>
>   - This also paves way for some other tricks that the original version
>   used to avoid overflows, e.g., start_time was almost only useful before
>   to make sure the sampled timestamp won't overflow a 32-bit field.
>
>   - This prepares further reports on top of existing data collected,
>   e.g. average page fault latencies.  When average operation is taken into
>   account, milliseconds are simply too coarse grained.
>
> When at it:
>
>   - Rename page_fault_vcpu_time to vcpu_blocktime_start.
>
>   - Rename vcpu_blocktime to vcpu_blocktime_total.
>
>   - Touch up the trace-events to not dump blocktime ctx pointer
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>