Messages in this thread | | | Date | Wed, 18 Dec 2013 15:11:25 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units |
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On Wed, Dec 18, 2013 at 04:01:04PM +0200, Alexander Shishkin wrote: > > Why don't you start by explaining _why_ you need a second stream to > > begin with? > > Oh, I'm sure I've explained it earlier ([1], [2])
See, I didn't read 0 because that information gets lost and patches should be self explanatory, and i didn't get to the Intel driver yet because well, I got stuck in the generic code.
> but why not. The data > in the second stream is generated at a rate which is hundreds of > megabytes per second per core. Decoding this data is ~1000 times slower > than generating it. Ergo, can't be done in kernel, needs to be exported > as-is to userspace for later retreival and decoding. Doing it via perf > stream means an extra copy, which at these rates is a waste. Ergo, a > second buffer.
Still confused, if you cannot copy it into one buffer, then why can you copy it into a second buffer?
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