On Mon, Dec 16, 2013 at 04:26:31PM +0800, Alex Shi wrote: > On 12/14/2013 10:19 PM, 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(). > > I am sorry if I miss sth. :) > > But if my understand correct, in the example of gup_fast, wait_split_huge_page > will never goes to BUG_ON(). Since the flush TLB IPI still be sent out to clear > each of _PAGE_SPLITTING on each CPU core. This patch just stop repeat TLB flush > in another SMT on same core. If there only noe SMT affected, the flush still be > executed on it. This has nothing what so ff'ing ever to do with huge pages. -- 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>