Messages in this thread | | | Subject | Re: [RFC PATCH 0/2] powerpc: CPU cache op cleanup | From | Benjamin Herrenschmidt <> | Date | Wed, 16 Nov 2011 10:46:32 +1100 |
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On Tue, 2011-11-15 at 16:45 -0600, Moffett, Kyle D wrote:
> I guess that's doable, although I have to admit that idea almost gives > me more of a headache than trying to fix up the 32-bit ASM. > > One thing that bothers me in particular is that both 32/64 versions of > __copy_tofrom_user() are dramatically overcomplicated for what they > ought to be doing. > > It would seem that if we get a page fault during an unaligned copy, we > ought to just give up and fall back to a simple byte-by-byte copy loop > from wherever we left off. That would eliminate 90% of the ugly > special cases without actually hurting performance, right? > > For a page-fault during a cacheline-aligned copy, we should be able to > handle the exception and retry from the last cacheline without much > logic, again with good performance. > > With that said, I'm curious about the origin of the PPC32 ASM. In > particular, it looks like it was generated by GCC at some point in the > distant past, and I'm wondering if there's a good way to rewrite that > file in C and trick GCC into generating the relevant exception tables > for it?
There is some serious history in there :-)
I would check with Anton, he's been doing some performance work on those lately (the 64-bit ones).
It's probably worth throwing a proof-of-concept simpler variant for 32-bit at least on the table and have people compare the perfs (typically network perfs). I can test on a range of ppc32 here (6xx, 7xxx, 4xx).
Cheers, Ben.
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