On 2026-06-14 17:19, H. Peter Anvin wrote:
> 
> OK, so v7.1 was released with this sizable performance regression. That 
> begs the question how to deal with it.
> 
> One option that might be reasonable for -stable is to simply add back 16 
> bytes of NOPs into the assembly file. However, that is obviously not a 
> long term fix.
> 

Okay, here is a hack that actually generates the proper alignment, and 
it DOES in fact fix the performance regression.

It uses the same hack as the Makefile to deal with function alignment 
with a prefix: it adds unnecessary NOPs so that the pre-alignment and 
post-alignment are the same. At the end of the day this really ought to 
be fixed in gcc.

This is not meant to be a final patch; this should go in a header file 
and be cleaned up etc, but I wanted to confirm that it does, in fact, 
fix the regression and that the alignment of x64_sys_call is the root 
cause of the problem.

PeterZ: at some point you and I talked about the following:

- Should x64_sys_call() be noinstr?
- If so, any reason we can't inline it into do_syscall_64()?
- Since we no longer use the sys_call_table[] as a jump table,
   do we actually need array_index_nospec()? in do_syscall_x64|32?

	-hpa