Re: Linux 2.6.32-rc1

Linus Torvalds
2009-09-30T16:14:57Z

On Wed, 30 Sep 2009, Eric Dumazet wrote:
>
> lock; cmpxchg8b (%%esi)
>
> gives 4 bytes opcode : f0 0f c7 0e
> Because alternative (call cmpxchg8b_emu) uses 5 bytes, a nop will be added.
>
> Choosing ".byte 0xf0, 0x0f, 0xc7, 0x4e, 0x00" aka "lock cmpxchg8b 0x0(%esi)" is a litle bit better ?

And if you want to be really clever, you would want to handle the non-SMP
case too, where you have just "cmpxchgb (%%esi)" (three bytes) without the
lock prefix.

However, at this point I think Arjan's patch is already way superior to
what we have now (feel free to take a look at what we generate on 32-bit
without PAE today - just have a barf-bag handy), so all I'd really want is
a few "tested-by"s to make me feel happier about it, and a few more people
looking at the emulation routine to all say "ok, looks sane, ACK".

And at that point we can then either make "cmpxchg()" just do the 8-byte
case natively, or just take your patch to change sched_clock.c to now use
the no-longer-entirely-disgusting cmpxchg64().

Ingo - I suspect both those patches should just go through you. You do
both x86 and scheduler, so I'll happily pull the end result.

Linus