Hello, Petr. On Thu, Dec 14, 2017 at 03:27:09PM +0100, Petr Mladek wrote: > Ah, I know that it was me who was pessimistic about Steven's approach[1] > and persuaded you that offloading idea was still alive. But I am less > sure now.
So, I don't really care which one gets in as long as the livelock problem is fixed although to my obviously partial eyes the two alternatives seem overly complex. That said, > My three main concerns about Steven's approach were: > > 1. I was afraid that it might introduce new type of deadlocks. > > But it seems that it is quite safe after all. > > > 2. Steven's code, implementing the hand shake, is far from trivial. > Few people were confused and reported false bugs. > > But the basic idea is pretty simple and straightforward. If > we manage to encapsulate it into few helpers, it might become > rather self-contained and maintainable. In each case, the needed > changes are much smaller than I expected. > > > 3. Soft-lockups are still theoretically possible with Steven's > approach. > > But it seems to be quite efficient in many real life scenarios, > including Tetsuo's stress testing. Or am I wrong? AFAICS, Steven's approach doesn't fix the livelock that we see quite often in the fleet where we don't have a safe context to keep flushing messages. This isn't theoretical at all. You simply don't have a safe context on the cpu to go to. I said I'd come back with a repro case but haven't had a chance to yet. I'll try to do it before the end of the year, but idk this is pretty obvious. Thanks. -- tejun
