On Tue, May 10, 2022 at 02:37:40PM +0900, Byungchul Park wrote: > Ted wrote: > > On Tue, May 10, 2022 at 09:32:13AM +0900, Byungchul Park wrote: > > > DEPT is tracking way more objects than Lockdep so it's inevitable to be > > > slower, but let me try to make it have the similar performance to > > > Lockdep. > > > > In order to eliminate some of these false positives, I suspect it's > > going to increase the number of object classes that DEPT will need to > > track even *more*. At which point, the cost/benefit of DEPT may get > > called into question, especially if all of the false positives can't > > be suppressed. > > Look. Let's talk in general terms. There's no way to get rid of the > false positives all the way. It's a decision issue for *balancing* > between considering potential cases and only real ones. Definitely, > potential is not real. The more potential things we consider, the higher > the chances are, that false positives appear. > > But yes. The advantage we'd take by detecting potential ones should be > higher than the risk of being bothered by false ones. Do you think a > tool is useless if it produces a few false positives? Of course, it'd > be a problem if it's too many, but otherwise, I think it'd be a great > tool if the advantage > the risk. > > Don't get me wrong here. It doesn't mean DEPT is perfect for now. The > performance should be improved and false alarms that appear should be > removed, of course. I'm talking about the direction. > > For now, there's no tool to track wait/event itself in Linux kernel - > a subset of the functionality exists tho. DEPT is the 1st try for that > purpose and can be a useful tool by the right direction. > > I know what you are concerning about. I bet it's false positives that > are going to bother you once merged. I'll insist that DEPT shouldn't be > used as a mandatory testing tool until considered stable enough. But > what about ones who would take the advantage use DEPT. Why don't you > think of folks who will take the advantage from the hints about > dependency of synchronization esp. when their subsystem requires very > complicated synchronization? Should a tool be useful only in a final > testing stage? What about the usefulness during development stage? > > It's worth noting DEPT works with any wait/event so any lockups e.g. > even by HW-SW interface, retry logic or the like can be detected by DEPT > once all waits and events are tagged properly. I believe the advantage > by that is much higher than the bad side facing false alarms. It's just > my opinion. I'm goning to respect the majority opinion. s/take advantage/have the benefit/g Byungchul
