Messages in this thread |  | | Date | Tue, 10 Oct 2000 19:38:33 +0200 | From | Jamie Lokier <> | Subject | Re: {PATCH] Re: wasting time on page fault |
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Linus Torvalds wrote: > > 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. > > Note that some of them are not very good no-ops. At least at some point > the "long" no-op was > > lea 0x00000000(%esi),%esi > > and you could cause AGI stalls and non-pairing with two of them in a row - > making the long no-op sequence potentially quite slow.
When it must emit two no-ops in a row, it uses %esi and then %edi so there's no AGI from that. However, the assembler doesn't check preceding instructions to pick a decent register for the no-op instruction. Solution: avoid writing to %esi before an alignment op.
> It may be that the special "lea" no-op is also recognized as such in newer > CPU's, but it wasn't in the early ones.
Does Crusoe recognise that? :-)
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