Date: Thu, 14 Dec 2000 09:58:20 -0800 (PST) From: John Baldwin <jhb@FreeBSD.ORG> To: Julian Elischer <julian@elischer.org> Cc: smp@FreeBSD.ORG Subject: RE: Mutex roadmap Message-ID: <XFMail.001214095820.jhb@FreeBSD.org> In-Reply-To: <3A38E440.B89DA298@elischer.org>
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On 14-Dec-00 Julian Elischer wrote:
> In my attempts to understand locking on behaplf of netgraph, I
> ended up writing up this little roadmap of where things are...
>
> In the hope that SOMEONE finds it useful, I'm posting it here.
Some corrections: :)
> ============== Macros that implement assembler locking primatives ====
> I'm not sure where these are used (I couldn't find any users).
> Or if they are compatible with the other stuff... are they coming of going?
MTX_EXIT is used in fork_trampoline() on the x86, and in switch_trampoline() on
the alpha and ia64. This specific instance of MTX_EXIT will hopefully be moved
out to a MI C function fork_trampoline() that returns to a very short MD stub
fork_return in asm.
> MTX_ENTER() Macro for non recursive spinlocks. (appears unused)
> alpha/include/mutex.h
> ia64/include/mutex.h
> i386/include/mutex.h
Just say 'machine/mutex.h', as it is more concise. :)
> ========= Standard MI atomic ops. Defined per processor.==============
> atomic stuff defined in {ia64,alpha,i386}/include/atomic.h
> largely by macros tha produce inline asm functions.
> only i386 examples detailed here.
> Note that on the alpha "compare and set" is quite expensive
> as it takes about 10 instructions. maybe we should use a different
> primative..
On the alpha all of the atomic ops are built from checked loads and conditional
stores. It's a RISC chip and doesn't have a 'semaphore' instruction like
'cmpxchg' or 'fetchadd' AFAIK.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.Baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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