On 8/15/24 23:44, Olivier Langlois wrote:
On Thu, 2024-08-15 at 18:17 -0400, Olivier Langlois wrote:
To my eyes, what is really important, it is that absolute best
technical solution is choosen and the only way that this discussion
can
be done, it is with numbers. So I have created a small created a
small
benchmark program to compare a function pointer indirect call vs
selecting a function in a 3 branches if/else if/else block. Here are
the results:
FWIW, it's just one branch / two different options in this case.
We shouldn't be doing a call if napi has never been requested,
so napi_dont_do_anything callback is not an option.
----------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------
BM_test_virtual 0.628 ns 0.627 ns 930255515
BM_test_ifElse 1.59 ns 1.58 ns 446805050
I have fixed my benchmark:
----------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------
BM_test_virtual 2.57 ns 2.53 ns 277764970
BM_test_ifElse 1.58 ns 1.57 ns 445197861
You passed the compiler flags for mitigations, right?
-mindirect-branch=thunk -mfunction-return=thunk -mindirect-branch-register
Regardless of overhead, my concern is the complexity and
amount of extra code. It's just over engineered. It's like
adding a virtual templated hierarchy of classes just to
implement a program that prints "2".
I pushed what I had (2 last patches), you can use it as a
reference, but be aware that it's a completely untested
draft with some obvious problems and ugly uapi.
https://github.com/isilence/linux.git manual-napi
https://github.com/isilence/linux/commits/manual-napi/
--
Pavel Begunkov
