On Tue, Feb 19, 2008 at 08:27:25AM -0600, Jack Steiner wrote: > > On Tue, Feb 19, 2008 at 02:58:51PM +0100, Andrea Arcangeli wrote: > > > understand the need for invalidate_begin/invalidate_end pairs at all. > > > > The need of the pairs is crystal clear to me: range_begin is needed > > for GRU _but_only_if_ range_end is called after releasing the > > reference that the VM holds on the page. _begin will flush the GRU tlb > > and at the same time it will take a mutex that will block further GRU > > tlb-miss-interrupts (no idea how they manange those nightmare locking, > > I didn't even try to add more locking to KVM and I get away with the > > fact KVM takes the pin on the page itself). > > As it turns out, no actual mutex is required. _begin_ simply increments a > count of active range invalidates, _end_ decrements the count. New TLB > dropins are deferred while range callouts are active. > > This would appear to be racy but the GRU has special hardware that > simplifies locking. When the GRU sees a TLB invalidate, all outstanding > misses & potentially inflight TLB dropins are marked by the GRU with a > "kill" bit. When the dropin finally occurs, the dropin is ignored & the > instruction is simply restarted. The instruction will fault again & the TLB > dropin will be repeated. This is optimized for the case where invalidates > are rare - true for users of the GRU.
OK (thanks to Robin as well). Now I understand why you are using it, but I don't understand why you don't defer new TLBs after the point where the linux pte changes. If you can do that, then you look and act much more like a TLB from the point of view of the Linux vm. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
