Re: [Qemu-devel] [RFC] host and guest kernel trace merging

[Peter Xu]

On Thu, Mar 24, 2016 at 10:13:17AM +0000, Stefan Hajnoczi wrote:
> There are probably race conditions if the tsc offset is queried
> independently from the trace collection.  For example, imagine the host
> is suspend right when tracing begins.  I think the TSC could be adjusted
> when the host wakes up again.

Right... So maybe we should never allow tsc-offset change
(e.g. suspend) happen during host-guest tracing?  It seems more like
a question about "whether we can do a merge", rather than "read a
correct offset"... If it changes, we cannot do the merge any more
(only if we record the offset for each guest entry)...

> 
> Ideally the TSC information would be part of the trace data so that
> there are no race conditions when interpeting time stamps.

Agree. We should keep the tsc-offset in the trace data.

Thanks.

-- peterx