On Mon, Feb 06, 2017 at 06:05:29PM +0200, Alexander Shishkin wrote: > Andi Kleen <[email protected]> writes: > > > Alexander Shishkin <[email protected]> writes: > > > >> Now that Intel PT supports more types of trace content than just branch > >> tracing, it may be useful to allow the user to disable branch tracing > >> when it is not needed. > >> > >> The special case is BDW, where not setting BranchEn is not supported. > >> > >> This is slightly trickier than necessary, because up to this moment > >> the driver has been setting BranchEn automatically and the userspace > >> assumes as much. Instead of reversing the semantics of BranchEn, we > >> introduce a 'passthrough' bit, which will forego the default and allow > >> the user to set BranchEn to their heart's content. > > > > cpu/passthrough=1,branchen=1/ seems far uglier/more complicanted to me > > than the original cpu/nobranch=1/ > > It's /passthrough=1,branch=0/ or simply /passthrough=1/.
Ok, but still you have to list exactly to which flags passthrough applies to, and it will only ever be branchen. So basically you turned nobranch=1 into two more difficult to explain flags without any future advantage. That is why nobranch=1 is better. It is far easier to explain and logical to the user. -Andi
