Re: [PATCH 0/8] perf: add ability to sample physical data addresses

Peter Zijlstra
2013-06-28T09:59:13Z

On Wed, Jun 26, 2013 at 09:10:50PM +0200, Stephane Eranian wrote:
> After more investigation with the author of the false sharing
> detection tool, I think
> that if the mapping changes, it is okay. The tool can detect this and
> drop the analysis
> at that address. So as long as we can flag the mapping change, we are
> okay. Hopefully,
> it does not occur frequently. If so, then I think there are bigger
> issues to fix on the system
> than false sharing.

But if you index everything using dev:inode:offset it doesn't matter if the
mapping changes; you're invariant to map placement.

And the thing is; we already compute most of that anyway in order to find the
code in DSOs, except there we use filename instead of dev:inode. However if
there were means to open files using dev:inode that might actually be more
reliable than using the filename.