Re: {PATCH] Re: wasting time on page fault

From: Jamie Lokier (
Date: Tue Oct 10 2000 - 04:28:49 EST

Andi Kleen wrote:
> > 1. Move the error_code block from divide_error to page_fault;
> > this removes one jump from the page_fault path.
> It is not clear that it is worth it. You want to align error_code and
> page_fault to 16 or 32 bytes bytes at least, and it would need to execute
> some nops depending on the length for fallthrough
> The jmp may be actually faster.

The assembler doesn't use nops for alignment -- it inserts longer
instructions that are effectively nops, either 1 or two. For larger
stretches, the assembler inserts a jmp itself for alignment.

Regardless, I'd expect the page_fault path to occur far more often than
any of the other fault/exception handlers that lead to error_code. So
much more that not aligning error_code is probably the right thing to do.

-- Jamie
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