Re: [patch] Real-Time Preemption, -VP-2.6.9-rc4-mm1-U0

[Karim Yaghmour]

Ingo Molnar wrote:
> i just added something ad-hoc.

Yes, I understood as much. I'm suggesting it because a lot of
people who need such ad-hoc functionality could easily be
using relayfs.

> I wanted it to be accurate across
> interrupt entries. I have not looked at the relayfs locking but how does
> it solve that?

cmpxchg (basically: try reserve; if fail retry; else write),
with per-cpu buffers.

> Also, cli/sti makes it obviously SMP-safe and is pretty
> cheap on all x86 CPUs. (Also, i didnt want to use preempt_disable/enable
> because the tracer interacts with that code quite heavily.)

No preempt_disable/enable found in the lockless logging in relayfs.

Karim
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