Re: smp_call_function_single lockups

[Linus Torvalds]

On Wed, Apr 1, 2015 at 2:59 PM, Chris J Arges
<chris.j.arges@xxxxxxxxxxxxx> wrote:
>
> It is worthwhile to do a 'bisect' to see where on average it takes
> longer to reproduce? Perhaps it will point to a relevant change, or it
> may be completely useless.

It's likely to be an exercise in futility. "git bisect" is realyl bad
at "gray area" things, and when it's a question of "it takes hours or
days to reproduce", it's almost certainly not worth it. Not unless
there is some really clear cut-off that we can believably say "this
causes it to get much slower". And in this case, I don't think it's
that clear-cut. Judging by DaveJ's attempts at bisecting things, the
timing just changes. And the differences might be due to entirely
unrelated changes like cacheline alignment etc.

So unless we find a real clear signature of the bug (I was hoping that
the ISR bit would be that sign), I don't think trying to bisect it
based on how quickly you can reproduce things is worthwhile.

                        Linus
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