Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata
From: Nick Piggin
Date: Mon Sep 15 2003 - 03:36:21 EST
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.
There are systems
where memory matters, but spending a week chasing 300 bytes when you can
knock out 50K is a waste of everyones time. Do the 40K problems first
The 'select a single CPU to support and/optimise for' -> 'select a
bitmap of CPUs to support' work is being done anyway though, so this
is more or less just one single IFDEF, which is more like a few
seconds work, rather than a week.
While I like Adrian's patch a lot from a functionality and user
simplicity point of view, the key to getting it merged is not to
increase the complexity of the implementation. The only objections to
the concept came from people who didn't understand it AFAIK.
And too many combinations of ill defined things like this will make
people (developers) go nuts.
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