Re: a joint letter on low latency and Linux

[Paul Barton-Davis]

First:

I need to apologize for Ingo for not contacting you before we sent
this letter. I intended to do so, but when it came time to actually
mail it out, I forgot that this was a prior step I had mentally
committed to taking. It would have been the right thing to do, and I
am sincerely sorry that it was not done.

That said, Ingo writes:

>> However, it turns out, as best we can gather, that you were not happy
>> with the basic structure of some or all of Ingo's low latency work.
>> [...]
>
>*I* was unhappy with the structure of that patch to begin with. The patch
>is ugly and unacceptable (read: a kludge) for inclusion into the
>mainstream kernel, period. I also said that i'll send a similar patch for
>2.4 as well, once the 2.4 codebase stabilizes. (right now we still have a
>high flux of fixes coming in - but i'll soon port the patch to 2.4)
>
>so please, do not make this appear as some 'fault' of Linus. Linus is
>rightfully (and thankfully) watching the quality of the mainstream kernel,
>and ugly patches are simply not accepted, regardless of the usefulness of
>a given patch. In fact it's my fault of not submitting those patches in a
>saner way. I'll fix this in the coming weeks.

I am a little confused, Ingo. There were several exchanges that you
had with Linus about the patches in which you put forward several
arguments in favor of their inclusion. These culminated in Linus
saying point blank that he would not do so.

Although there is an argument that some of the later patches went too
far (e.g. adding code to spinlock functions), I think that the basic
structure of your code (not the source, but the notion of adding
preemption points at locations that were identifiable problems in
linux' latency behaviour) was thought by several people to be a good
solution. Everything I have read from Linus has suggested to me
that he thinks that this is a bad way to solve the latency issues. 

I don't have much to say about the specific nature of the code in the
patches, but my understanding was that this wasn't the reason for
Linus' not liking them.

--p