On Tue, May 10, 2022 at 07:07:25PM +0200, Uros Bizjak wrote: > On Tue, May 10, 2022 at 6:55 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > On Tue, May 10, 2022 at 05:42:17PM +0200, Uros Bizjak wrote: > > > This patch adds try_cmpxchg64 to improve code around cmpxchg8b. While > > > the resulting code improvements on x86_64 are minor (a compare and a move saved), > > > the improvements on x86_32 are quite noticeable. The code improves from: > > > > What user of cmpxchg64 is this? > > This is cmpxchg64 in pi_try_set_control from > arch/x86/kvm/vmx/posted_intr.c, as shown in a RFC patch [1]. I can't read that code, my brain is hard wired to read pi as priority inheritance/inversion. Still, does 32bit actually support that stuff? > There are some more opportunities for try_cmpxchg64 in KVM, namely > fast_pf_fix_direct_spte in arch/x86/kvm/mmu/mmu.c and > tdp_mmu_set_spte_atomic in arch/x86/kvm/mmu/tdp_mmu.c tdp_mmu is definitely 64bit only and as such shouldn't need to use cmpxchg64. Anyway, your patch looks about right, but I find it *really* hard to care about 32bit code these days.
