On Tue, 28 Oct 2025 09:42:25 -0700 Kuniyuki Iwashima <[email protected]> wrote:
> On Tue, Oct 28, 2025 at 2:54 AM David Laight > <[email protected]> wrote: > > > > On Tue, 28 Oct 2025 05:32:13 +0000 > > Kuniyuki Iwashima <[email protected]> wrote: > > > > .... > > > I rebased on 19ab0a22efbd and tested 4 versions on > > > AMD EPYC 7B12 machine: > > > > That is zen5 which I believe has much faster clac/stac than anything else. > > (It might also have a faster lfence - not sure.) > > This is the Zen 2 platform, so probably the stac/clac cost will be > more expensive than you expect on Zen 5. I must has looked the cpu type incorrectly. AMD haven't made it easy working out the cpu architecture. I need to get an older zen cpu for my set of test systems (and some newer Intel ones). > > Getting a 3% change for that diff also seems unlikely. > > Even if you halved the execution time of that code the system would have > > to be spending 6% of the time in that loop. > > Even your original post only shows 1% in ep_try_send_events(). I realised after that you might be showing a 3% change in that 1%. > > We saw a similar improvement on the same platform by > 1fb0e471611d ("net: remove one stac/clac pair from > move_addr_to_user()"). Certainly removing one could easily be measurable. David
