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[Bug runtime/3858] option to share trace buffers between probe modules
- From: "hunt at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sources dot redhat dot com
- Date: 18 Oct 2007 14:06:45 -0000
- Subject: [Bug runtime/3858] option to share trace buffers between probe modules
- References: <20070111113517.3858.masami.hiramatsu.pt@hitachi.com>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From hunt at redhat dot com 2007-10-18 14:06 -------
(In reply to comment #16)
> Interesting solution (using module-exported functions from the host module)!
> Martin, if you have no objection, let's go ahead.
We have discussed this approach before and I am fine with it.
> One additional consideration for testing/checking: this now makes it theoretically
> possible for distinct probes to call into one particular probe module's runtime
> at the same time. Even though this is limited to the I/O functions, can you
> cover whether any additional mutual exclusion may be necessary? Even on per-cpu
> buffers, we have situations where probes don't run atomically any more ("begin"
> probes that don't block interrupts, only preemption). So if the host does a
>
> probe begin { while(i++<1000) { log ("lots of stuff") } }
>
> at the same time the guest does
>
> probe timer.profile { log ("some stuff") }
>
> then could we have a problem?
Ouch. As soon as I read that I realized we currently have a problem with
begin/end probes. See http://sourceware.org/bugzilla/show_bug.cgi?id=5194
For the buffer sharing, I think the problem is simply that output will get mixed
together in such situations, which is not unexpected in a shared buffer situation.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=3858
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