Re: [RFT/PATCH v2 2/6] x86-64: Optimize vread_tsc's barriers

Andi Kleen
2011-04-07T16:42:50Z

> But before that, I would check that the second lfence is needed AT
> ALL. I don't know whether we ever tried the "only barrier before"
> version, because quite frankly, if you call this thing in a loop, then

> a single barrier will still mean that there are barriers in between
> iterations. So...

The testers will call it in a loop, but real users (e.g. using it for
a logging timestamp) may not.

I'm sure a single barrier would have fixed the testers, as you point out,
but the goal wasn't to only fix testers.

-Andi
--
ak@linux.intel.com -- Speaking for myself only.