Messages in this thread | | | Date | Mon, 5 Oct 2009 11:24:53 +0200 | Subject | Re: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters | From | Frédéric Weisbecker <> |
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2009/10/5 Ingo Molnar <mingo@elte.hu>: > > * Peter Zijlstra <peterz@infradead.org> wrote: >> Non-trivial. >> >> Something like this would imply a single output channel for all these >> CPUs, and we've already seen that stuffing too many CPUs down one such >> channel (using -M) leads to significant performance issues. > > We could add internal per cpu buffering before it hits any globally > visible output channel. (That has come up when i talked to Frederic > about the function tracer.) We could even have page sized output (via > the introduction of a NOP event that fills up to the next page edge).
That looks good for the counting/sampling fast path, but would that scale once it comes to reordering in the globally visible output channel? Such a union has its costs.
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