Messages in this thread | | | Date | Mon, 15 Sep 2003 19:58:39 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata |
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John Bradford wrote:
>>>>>That's a non-issue. 300 bytes matters a lot on some systems. The >>>>>fact that there are drivers that are bloated is nothing to do with >>>>>it. >>>>> >>>>> >>>>Its kind of irrelevant when by saying "Athlon" you've added 128 byte >>>>alignment to all the cache friendly structure padding. >>>> >>>> >>>My intention is that we won't have done 128 byte alignments just by >>>'supporting' Athlons, only if we want to run fast on Athlons. A >>>distribution kernel that is intended to boot on all CPUs needs >>>workarounds for Athlon bugs, but it doesn't need 128 byte alignment. >>> >>>Obviously using such a kernel for anything other than getting a system >>>up and running to compile a better kernel is a Bad Thing, but the >>>distributions could supply separate Athlon, PIV, and 386 _optimised_ >>>kernels. >>> >>> >>Why bother with that complexity? Just use 128 byte lines. This allows >>a decent generic kernel. The people who have space requirements would >>only compile what they need anyway. >> > >So, basically, if you compile a kernel for a 386, but think that maybe >one day you might need to run it on an Athlon for debugging purposes, >you use 128 byte padding, because it's not too bad on the 386? Seems >pretty wasteful to me when the obvious, simple, elegant solution is to >allow independent selection of workaround inclusion and optimisation. >Especially since half of the work has already been done. >
I missed the "simple, elegant" part. Conceptually elegant maybe.
If you mean to use the optimise option only to set cache line size, then that might be a bit saner.
As far as the case study goes though: if you were worried about being wasteful, why wouldn't you compile just for the 386 and debug from that?
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