On Thu, Feb 15, 2024 at 07:39:15PM -0500, Steven Rostedt wrote: > On Thu, 15 Feb 2024 19:32:38 -0500 > Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > > > > But where are the benchmarks that are not micro-benchmarks. How much > > > overhead does this cause to those? Is it in the noise, or is it noticeable? > > > > Microbenchmarks are how we magnify the effect of a change like this to > > the most we'll ever see. Barring cache effects, it'll be in the noise. > > > > Cache effects are a concern here because we're now touching task_struct > > in the allocation fast path; that is where the > > "compiled-in-but-turned-off" overhead comes from, because we can't add > > static keys for that code without doubling the amount of icache > > footprint, and I don't think that would be a great tradeoff. > > > > So: if your code has fastpath allocations where the hot part of > > task_struct isn't in cache, then this will be noticeable overhead to > > you, otherwise it won't be. > > All nice, but where are the benchmarks? This looks like it will have an > affect on cache and you can talk all you want about how it will not be an > issue, but without real world benchmarks, it's meaningless. Numbers talk. Steve, you're being demanding. We provided sufficient benchmarks to show the overhead is low enough for production, and then I gave you a detailed breakdown of where our overhead is and where it'll show up. I think that's reasonable.
