On Sat, Dec 14, 2013 at 03:19:02PM +0100, Peter Zijlstra wrote: > On Fri, Dec 13, 2013 at 10:11:05AM +0800, Alex Shi wrote: > > BTW, > > A bewitching idea is till attracting me. > > https://lkml.org/lkml/2012/5/23/148 > > Even it was sentenced to death by HPA. > > https://lkml.org/lkml/2012/5/24/143 > > > > That is that just flush one of thread TLB is enough for SMT/HT, seems > > TLB is still shared in core on Intel CPU. This benefit is unconditional, > > and if my memory right, Kbuild testing can improve about 1~2% in average > > level. > > > > So could you like to accept some ugly quirks to do this lazy TLB flush > > on known working CPU? > > Forgive me if it's stupid. > > I think there's a further problem with that patch -- aside of it being > right from a hardware point of view. > > We currently rely on the tlb flush IPI to synchronize with lockless page > table walkers like gup_fast(). > > By not sending an IPI to all CPUs you can get into trouble and crash the > kernel. > > We absolutely must keep sending the IPI to all relevant CPUs, we can > choose not to actually do the flush on some CPUs, but we must keep > sending the IPI. The alternative is switching x86 over to use HAVE_RCU_TABLE_FREE. -- 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>