On Wed, 30 Oct 2024 00:16:48 +0000, Raghavendra Rao Ananta <rananta@xxxxxxxxxx> wrote: > > On Tue, Oct 29, 2024 at 11:47 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > On Tue, 29 Oct 2024 17:06:09 +0000, > > Raghavendra Rao Ananta <rananta@xxxxxxxxxx> wrote: > > > > > > On Tue, Oct 29, 2024 at 9:27 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > > > > > On Mon, 28 Oct 2024 23:45:33 +0000, > > > > Raghavendra Rao Ananta <rananta@xxxxxxxxxx> wrote: > > > > > > > > > Did you have a chance to check whether this had any negative impact on > > > > actual workloads? Since the entry/exit code is a bit of a hot spot, > > > > I'd like to make sure we're not penalising the common case (I only > > > > wrote this patch while waiting in an airport, and didn't test it at > > > > all). > > > > > > > I ran the kvm selftests, kvm-unit-tests and booted a linux guest to > > > test the change and noticed no failures. > > > Any specific test you want to try out? > > > > My question is not about failures (I didn't expect any), but > > specifically about *performance*, and whether checking the flag > > without a static key can lead to any performance drop on the hot path. > > > > Can you please run an exit-heavy workload (such as hackbench, for > > example), and report any significant delta you could measure? > > Oh, I see. I ran hackbench and micro-bench from kvm-unit-tests (which > also causes a lot of entry/exits), on Ampere Altra with kernel at > v6.12-rc1, and see no significant difference in perf. Thanks for running this stuff. > timer_10ms 231040.0 902.0 > timer_10ms 234120.0 914.0 This seems to be the only case were we are adversely affected by this change. In the grand scheme of thins, that's noise. But this gives us a clear line of sight for the removal of the in-kernel interrupts back to userspace. Thanks, M. -- Without deviation from the norm, progress is not possible.
