Messages in this thread | | | Date | Tue, 02 Oct 2007 13:51:22 -0400 | From | "Alan D. Brunelle" <> | Subject | Re: Linux Kernel Markers - performance characterization with large IO load on large-ish system |
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Mathieu Desnoyers wrote: >> remember that we have seen and discussed something like this before, >> it's still a puzzle to me... >> >> > I do wonder about that performance _increase_ with blktrace enabled. I > > Interesting question indeed. > > In those tests, when blktrace is running, are the relay buffers only > written to or they are also read ? >
blktrace (the utility) was running too - so the relay buffere /were/ being read and stored out to disk elsewhere.
> Running the tests without consuming the buffers (in overwrite mode) > would tell us more about the nature of the disturbance causing the > performance increase. >
I'd have to write a utility to enable the traces, but then not read. Let me think about that.
> Also, a kernel trace could help us understand more thoroughly what is > happening there.. is it caused by the scheduler ? memory allocation ? > data cache alignment ? >
Yep - when I get some time, I'll look into that. [Clearly not a gating issue for marker support...]
> I would suggest that you try aligning the block layer data structures > accessed by blktrace on L2 cacheline size and compare the results (when > blktrace is disabled). >
Again, when I get some time! :-)
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