Messages in this thread | | | Date | Wed, 21 May 2008 12:44:07 -0700 (PDT) | From | Trent Piepho <> | Subject | Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code |
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On Wed, 21 May 2008, Benjamin Herrenschmidt wrote: >> Depends on what you define as "necessary". It's seem clear that I/O accessors >> _no not_ need to be strictly ordered with respect to normal memory accesses, >> by what's defined in memory-barriers.txt. So if by "necessary" you mean what >> the Linux standard for I/O accessors requires (and what other archs provide), >> then yes, they have the necessary ordering guarantees. >> >> But, if you want them to be strictly ordered w.r.t to normal memory, that's >> not the case. > > They should be.
Someone should update memory-barriers.txt, because it doesn't say that, and all I/O accessors for all the arches, because none of them are.
>> Here's a quick hack I stuck in a driver to test. compile with -save-temps and >> check the resulting asm. gcc will do the optimization I described above. >> >> static void __iomem *baz = (void*)0x1234; >> static struct bar { >> u32 bar[256]; >> } bar; >> >> void foo(void) { >> bar.bar[0] = 44; >> out_be32(baz+100, 200); >> bar.bar[0] = 45; >> out_be32(baz+101, 201); >> } > > Have you removed -fno-strict-aliasing ? Just don't do that.
No, it's compiled with a normal kernel build, which includes -fno-strict-aliasing.
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