Messages in this thread | | | Subject | Re: [patch 1/2] x86_64 page fault NMI-safe | From | Peter Zijlstra <> | Date | Wed, 04 Aug 2010 16:56:28 +0200 |
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On Wed, 2010-08-04 at 10:45 -0400, Mathieu Desnoyers wrote:
> How do you plan to read the data concurrently with the writer overwriting the > data while you are reading it without corruption ?
I don't consider reading while writing (in overwrite mode) a valid case.
If you want to use overwrite, stop the writer before reading it.
> I think that the stack dump > should simply be saved directly to the ring buffer, without copy. The > dump_stack() functions might have to be extended so they don't just save text > dumbly, but can also be used to save events into the trace in binary format, > perhaps with the continuation cookie Linus was proposing.
Because I don't want to support truncating reservations (because that leads to large nops for nested events) and when the event needs to go to multiple buffers you can re-use the stack-dump without having to do the unwind again.
The problem with the continuation thing Linus suggested is that it would bloat the output 3 fold. A stack entry is a single u64. If you want to wrap that in a continuation event you need: a header (u64), a cookie (u64) and the entry (u64).
Continuation events might make heaps of sense for larger data pieces, but I don't see them being practical for such small pieces.
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