fche changed the topic of #systemtap to: http://sourceware.org/systemtap; email systemtap@sourceware.org if answers here not timely, conversations may be logged
<lightydo>
the results vary with each run (stap) but remain significantly inferior (copied, 1.29942 s, 3.3 GB/s, copied, 1.47352 s, 2.9 GB/s)
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<mjw>
lightydo, Looks like a worst case scenario. I would play with the bs and count and see how it affects things. What happens for example of you swap them? bs=1M count=4K and/or use real files.
<lightydo>
will try that..
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<lightydo>
mjw, indeed you are right. the performance hit is much lower when inverting bs and count values
<mjw>
but yeah, there is some overhead to probing, the example you use seems to insert 2 million probe interrupts, which is probably noticeable.
<mjw>
If you swap the arguments there are probably only ~10000 probe interrupts, which should be less noticeable.
<mjw>
stap -t will give you some statistics
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<fche>
it'd also help if the kernel offered tracepoints at the vfs operations, so we wouldn't have to suffer full kprobes hits
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