Thanks for looking into it.
I have tried to reproduce the slowdown on Ubuntu with Emacs 28 and 27.2 and compared against my current patched 27.1 Emacs. The conclusion is that something improved in a recent version of Emacs and the patch is not moving the needle on this.
There is still a super-liner cost somewhere. But as a user I only hit this when accidentally displaying a large file, and current behavior is interactive enough that I can kill the process running in the shell.
Once I get a chance I would also like to try on Mac OS X where the problem was more pronounced.
Thanks,
Anton
|--------------------+---------------------------------------+----------------|
| GNU Emacs 27.2 | time python3 -c 'print("x"*1024*256)' | real 0m20.805s |
| GNU Emacs 28.0.50 | time python3 -c 'print("x"*1024*32)' | real 0m0.315s |
| GNU Emacs 28.0.50 | time python3 -c 'print("x"*1024*64)' | real 0m1.151s |
| GNU Emacs 28.0.50 | time python3 -c 'print("x"*1024*128)' | real 0m6.168s |
| GNU Emacs 28.0.50 | time python3 -c 'print("x"*1024*256)' | real 0m22.153s |
| GNU Emacs 27.1* | time python3 -c 'print("x"*1024*32)' | real 0m0.237s |
| GNU Emacs 27.1* | time python3 -c 'print("x"*1024*64)' | real 0m1.108s |
| GNU Emacs 27.1* | time python3 -c 'print("x"*1024*128)' | real 0m5.172s |
| GNU Emacs 27.1* | time python3 -c 'print("x"*1024*256)' | real 0m24.369s |
| GNU Emacs 28.0.50* | time python3 -c 'print("x"*1024*32)' | real 0m0.234s |
| GNU Emacs 28.0.50* | time python3 -c 'print("x"*1024*64)' | real 0m0.978s |
| GNU Emacs 28.0.50* | time python3 -c 'print("x"*1024*128)' | real 0m4.716s |
| GNU Emacs 28.0.50* | time python3 -c 'print("x"*1024*256)' | real 0m19.047s |