On Fri, Jan 19, 2018 at 08:22:36PM +0200, Nikolay Borisov wrote: > > > On 19.01.2018 20:15, David Sterba wrote: > > On Fri, Jan 05, 2018 at 12:51:16PM -0700, Liu Bo wrote: > >> This is adding a tracepoint 'btrfs_handle_em_exist' to help debug the > >> subtle bugs around merge_extent_mapping. > >> > >> Signed-off-by: Liu Bo <bo.li....@oracle.com> > > > > Nikolay has some concernas about adding the tracepoint, so I'll leave > > this patch out of the series for now as we should decide how to proceed. > > > > Thacepoints are considered an ABI by some and not ABI by others. I think > > it's a good addition to the debugging aids that also may turn out to be > > useful for evaluating performance later. > > > > At minimum we could add some prefix/suffix to the debugging tracepoint > > name, so we can let developers add what they need right away. > My concern specifically has to do with the fact that if tracepoints are > considere ABI then whatever decision we make now will be cast in stone
Right, same as with the ioctls, we take a great care there and still do mistakes that get discovered months after. > and if we juggle the code around we will still have to retain the format > of the tracepoint. If, OTOH we are able to remove and change the > tracepoint as we see fit - then it's okay. Otherwise we risk polluting > the code Understood and agreed. Jeff raised a question if there are namespaces in the tracepoints. That's an interesting point and would be more systematic than inventing our own naming scheme. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
