[+Ricardo, as he wrote the original split walker] On Thu, Jul 18, 2024 at 10:35:19PM +0000, Colton Lewis wrote: > Moving the data barrier from stage2_split_walker to after the walk is > finished in kvm_pgtable_stage2_split results in a roughly 70% > reduction in Clear Dirty Log Time in dirty_log_perf_test (modified to > use eager page splitting) when using huge pages. This gain holds > steady through a range of vcpus used (tested 1-64) and memory > used (tested 1-64GB). > > This is safe to do because nothing else is using the page tables while > they are still being mapped and this is how other page table walkers > already function. None of them have a data barrier in the walker > itself. > > Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx> > --- > arch/arm64/kvm/hyp/pgtable.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 9e2bbee77491..9788af2ca8c0 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -1547,7 +1547,6 @@ static int stage2_split_walker(const struct kvm_pgtable_visit_ctx *ctx, > */ > new = kvm_init_table_pte(childp, mm_ops); > stage2_make_pte(ctx, new); > - dsb(ishst); > return 0; > } > > @@ -1559,8 +1558,11 @@ int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size, > .flags = KVM_PGTABLE_WALK_LEAF, > .arg = mc, > }; > + int ret; > > - return kvm_pgtable_walk(pgt, addr, size, &walker); > + ret = kvm_pgtable_walk(pgt, addr, size, &walker); > + dsb(ishst); > + return ret; > } This looks ok to me, but it would be great if Ricardo could have a look as well. Will
