On Fri, Jun 25, 2021, Peter Xu wrote: > Add a counter field into pte_list_desc, so as to simplify the add/remove/loop > logic. E.g., we don't need to loop over the array any more for most reasons. > > This will make more sense after we've switched the array size to be larger > otherwise the counter will be a waste. > > Initially I wanted to store a tail pointer at the head of the array list so we > don't need to traverse the list at least for pushing new ones (if without the > counter we traverse both the list and the array). However that'll need > slightly more change without a huge lot benefit, e.g., after we grow entry > numbers per array the list traversing is not so expensive. > > So let's be simple but still try to get as much benefit as we can with just > these extra few lines of changes (not to mention the code looks easier too > without looping over arrays). > > I used the same a test case to fork 500 child and recycle them ("./rmap_fork > 500" [1]), this patch further speeds up the total fork time of about 14%, which > is a total of 38% of vanilla kernel: > > Vanilla: 367.20 (+-4.58%) > 3->15 slots: 302.00 (+-5.30%) > Add counter: 265.20 (+-9.88%) > > [1] https://github.com/xzpeter/clibs/commit/825436f825453de2ea5aaee4bdb1c92281efe5b3 > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > --- > arch/x86/kvm/mmu/mmu.c | 33 ++++++++++++++++++--------------- > 1 file changed, 18 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 9b093985a2ef..ba0258bdebc4 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -138,10 +138,15 @@ module_param(dbg, bool, 0644); > #include <trace/events/kvm.h> > > /* make pte_list_desc fit well in cache lines */ > -#define PTE_LIST_EXT 15 > +#define PTE_LIST_EXT 14 Doh, I looked at kvm/queue code before looking at the full series. > struct pte_list_desc { > u64 *sptes[PTE_LIST_EXT]; > + /* > + * Stores number of entries stored in the pte_list_desc. No need to be > + * u64 but just for easier alignment. When PTE_LIST_EXT, means full. > + */ > + u64 spte_count; Per my feedback to the previous patch, this should be above sptes[] so that rmaps with <8 SPTEs only touch one cache line. No idea if it actually matters in practice, but I can't see how it would harm anything. > struct pte_list_desc *more; > };