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SubjectRe: [PATCH 4/4] ring-buffer: only allocate buffers for online cpus
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> > I don't like this patch.
> > your [1/4] and [2/4] already solve Pierre's problem.
> >
> > using online cpu (not possible cpu) increase performance overhead
> > and messiness.
> > but nobody get benefit ;)
>
> Well, the fact that you can have 15 buffers for non existent CPUs is a big
> benefit. And the overhead was only on the read side, not the write, and
> very limited in overhead for that matter.
>
> But, looking at this, I realized I can get rid of all the
> "get_online_cpus". I originally had the CPU_DOWN_PREPARE remove the
> buffer. But I found it highly annoying during tests, that I lose my data
> when I brought down a CPU. Thus, I removed the code to free the buffer and
> replaced it with the comment explaining this.
>
> The get_online_cpus is to prevent the race where we might remove a buffer.
> But since we do not do that anymore, those get_online_cpus are pretty
> useless.
>
> I'll update the code in a bit.

Great!

from mission critical area view, CPU down event is very important.
I don't hope to lost trace data of downed cpu.
and no get_online_cpus() don't cause annoy overhead.

I love to see your next patch :)




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