On 07/31, Frederic Weisbecker wrote: > > On Wed, Jul 30, 2014 at 10:23:34AM -0700, Andy Lutomirski wrote: > > > > At the end of the day, the syscall slowpath code calls a bunch of > > functions depending on what TIF_XYZ flags are set. As long as it's > > structured like "if (TIF_A) do_a(); if (TIF_B) do_b();" or something > > like that, it's comprehensible. But once random functions with no > > explicit flag checks or comments start showing up, it gets confusing. > > Yeah that's a point. I don't mind much the TIF_NOHZ test if you like. And in my opinion if (work & TIF_XYZ) user_exit(); looks even more confusing. Because, once again, TIF_XYZ is not the reason to call user_exit(). Not to mention this adds a minor performance penalty. > > If it's indeed all-or-nothing, I could remove the check and add a > > comment. But please keep in mind that, currently, the slow path is > > *slow*, and my patches only improve the entry case. So enabling > > context tracking on every task will hurt. > > That's what we do anyway. I haven't found a safe way to enabled context tracking > without tracking all CPUs. And if we change this, then the code above becomes racy. The state of TIF_XYZ can be changed right after the check. OK, it is racy anyway ;) but still this adds more confusion. I feel that TIF_XYZ must die. But yes, yes, I know that it is very simple to say this. And no, so far I do not know how we can improve this all. But again, again, I won't insist. Just another "can't resist" email, please ignore. Oleg.
