On Thu, 22 Jun 2017, Andy Lutomirski wrote: > On Thu, Jun 22, 2017 at 2:22 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > On Thu, 22 Jun 2017, Andy Lutomirski wrote: > >> On Thu, Jun 22, 2017 at 5:21 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > >> > Now one other optimization which should be trivial to add is to keep the 4 > >> > asid context entries in cpu_tlbstate and cache the last asid in thread > >> > info. If that's still valid then use it otherwise unconditionally get a new > >> > one. That avoids the whole loop machinery and thread info is cache hot in > >> > the context switch anyway. Delta patch on top of your version below. > >> > >> I'm not sure I understand. If an mm has ASID 0 on CPU 0 and ASID 1 on > >> CPU 1 and a thread in that mm bounces back and forth between those > >> CPUs, won't your patch cause it to flush every time? > > > > Yeah, I was too focussed on the non migratory case, where two tasks from > > different processes play rapid ping pong. That's what I was looking at for > > various reasons. > > > > There the cached asid really helps by avoiding the loop completely, but > > yes, the search needs to be done for the bouncing between CPUs case. > > > > So maybe a combo of those might be interesting. > > > > I'm not too worried about optimizing away the loop. It's a loop over > four or six things that are all in cachelines that we need anyway. I > suspect that we'll never be able to see it in any microbenchmark, let > alone real application. Fair enough. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
