On Tue, Jul 12, 2011 at 5:15 PM, Adam Leventhal <a...@delphix.com> wrote:
> Hey Bryan
>
>> Supporting a ring buffer policy is a tad brutal, because it would
>> require processing the entire ring to verify that the ECB isn't in it.
>> There are ways we could optimize that, but they're ugly; unless
>> someone is burning with this use case, I'd rather punt on it.
>> Anonymous tracing will just work; once the enabling is claimed, the
>> buffer will be switched, and it will become reapable.
>
> I actually meant a negative test case.
As I imagine you saw, there's already one there that uses speculative
tracing and verifies that enablings are not reaped:
usr/src/cmd/dtrace/test/tst/common/usdt/tst.noreap.ksh
Having a test that uses ring buffering is certainly possible, it's
just a more complicated test to write. (I'm currently cheating a bit
by using one enabling to kick off another.) But I'm happy to add it
if you'd like to see it...
>> Yes; you don't want to keep trying in perpetuity because you may be
>> blocked by either a ring buffer policy or speculative tracing or
>> something else that is managing to cache ECB state. So after a while,
>> you want to give up.
>
> Would that be worth a one- or two-line comment?
There's already the comment that it's padded out to avoid false
sharing; does it merit more than that?
- Bryan
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