On Thu, Jan 12, 2023 at 05:35:22PM -0300, Gabriel Krisman Bertazi wrote: > Breno Leitao <leitao@xxxxxxxxxx> writes: > > > This patch removes some "cold" fields from `struct io_issue_def`. > > > > The plan is to keep only highly used fields into `struct io_issue_def`, so, > > it may be hot in the cache. The hot fields are basically all the bitfields > > and the callback functions for .issue and .prep. > > > > The other less frequently used fields are now located in a secondary and > > cold struct, called `io_cold_def`. > > > > This is the size for the structs: > > > > Before: io_issue_def = 56 bytes > > After: io_issue_def = 24 bytes; io_cold_def = 40 bytes > > Does this change have an observable impact in run time? Did it show > a significant decrease of dcache misses? I haven't tested it. I expect it might be hard to came up with such test. A possible test might be running io_uring heavy tests, while adding enough memory pressure. Doing this in two different instant (A/B test), might be a unpredicable and the error deviation might hide the benefit.
