On Fri, May 06, 2022 at 03:12:32PM +0000, Honnappa Nagarahalli wrote: > <snip> > > > > On Thu, May 05, 2022 at 10:59:32PM +0000, Honnappa Nagarahalli wrote: > > > Thanks Stephen. Do you see any performance difference with this change? > > > > as a matter of due diligence i think a comparison should be made just to be > > confident nothing is regressing. > > > > i support this change in principal since it is generally accepted best > > practice to > > not force inlining since it can remove more valuable optimizations that the > > compiler may make that the human can't see. > > the optimizations may vary depending on compiler implementation. > > > > force inlining should be used as a targeted measure rather than blanket on > > every function and when in use probably needs to be periodically reviewed > > and > > potentially removed as the code / compiler evolves. > > > > also one other consideration is the impact of a particular compiler's force > > inlining intrinsic/builtin is that it may permit inlining of functions when > > not > > declared in a header. i.e. a function from one library may be able to be > > inlined > > to another binary as a link time optimization. although everything here is > > in a > > header so it's a bit moot. > > > > i'd like to see this change go in if possible. > Like Stephen mentions below, I am sure we will have a for and against > discussion here. > As a DPDK community we have put performance front and center, I would prefer > to go down that route first. >
I ran some initial numbers with this patch, and the very quick summary of what I've seen so far: * Unit tests show no major differences, and while it depends on what specific number you are interested in, most seem within margin of error. * Within unit tests, the one number I mostly look at when considering inlining is the "empty poll" cost, since I believe we should look to keep that as close to zero as possible. In the past I've seen that number jump from 3 cycles to 12 cycles due to missed inlining. In this case, it seem fine. * Ran a quick test with the eventdev_pipeline example app using SW eventdev, as a test of an actual app which is fairly ring-heavy [used 8 workers with 1000 cycles per packet hop]. (Thanks to Harry vH for this suggestion of a workload) * GCC 8 build - no difference observed * GCC 11 build - approx 2% perf reduction observed As I said, these are just some quick rough numbers, and I'll try and get some more numbers on a couple of different platforms, see if the small reduction seen is consistent or not. I may also test a few differnet combinations/options in the eventdev test. It would be good if others also tested on a few platforms available to them. /Bruce
