Re: Lisp_Marker size on 32bit systems

[Paul Eggert]

On 09/07/2018 05:16 AM, Stefan Monnier wrote:
> Where does this 20% slow down come from?

Ha! It was because the 16-byte alignment caused pure space to overflow, 
which disabled GC. No wonder there was such a big performance difference.

I fixed that, and now the patch to shrink marker allocations from 32 to 
24 bytes on x86 causes my standard benchmark (make compile-always) to 
run only 1.0% slower, which is more reasonable. A microbenchmark of 
running (make-marker) over and over again for 10,000,000 times runs 36% 
slower (815 vs 597 ns for a single call). So it still looks like we 
should be following GCC's max_align_t hint and using 16-byte alignment 
on x86, even though this wastes memory.

Maybe we should be using 4 mark bits instead of 3?