Messages in this thread | | | From | David Mosberger <> | Date | Tue, 6 Jul 2004 17:01:32 -0700 | Subject | Re: [PATCH] - Reduce TLB flushing during process migration |
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>>>>> On Fri, 2 Jul 2004 12:39:05 -0500, Jack Steiner <steiner@sgi.com> said:
>> Also, my preference would be for tlb_migrate_finish() to be a true no-op >> (not a call to a no-op function) when compiling for a platform that >> doesn't need this hook. Could you look into this?
Jack> For platforms that dont define their own tlb_migrate_finish, Jack> it is defined as :
Jack> #define tlb_migrate_finish(mm) do {} while (0)
Jack> I'm not sure if I understood your point above. This is Jack> consistent with other noop definitions (at least some of them) Jack> & should not generate any code.
Well, then it's not a true no-op. The other no-ops are all for init-type stuff, so they're not at all performance critical. Even when compiling a non-generic kernel, those no-op functions will be called. This is really a limitation in the current machvec-scheme. I think what we need is a way to explicitly declare a no-op callback, such that it can be optimized away completely for platforms that don't need it. Perhaps there could be something along the lines of:
#ifdef CONFIG_IA64_GENERIC # define machvec_noop(noop_function) noop_function #else # define machvec_noop(noop_function) /* empty */ #endif
Then you could do:
# define platform_tlb_migrate_finish machvec_noop(machvec_mm_noop)
I _think_ this should work, provided that callbacks that expand into true no-ops never have their address taken.
(This reminds me: in the no-op dummy routines in machvec.c should be named based on the type-signature they use, since it's possible to share no-op handlers for callbacks with the same type-signature; this is why I called the no-op machvec_mm_noop in the example above rather than machvec_tlb_migrate_finish as was the case in your patch).
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