Messages in this thread | | | Subject | Re: [RFC PATCH 0/4] perf: Custom contexts | From | Peter Zijlstra <> | Date | Wed, 16 Mar 2011 15:31:52 +0100 |
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On Wed, 2011-03-16 at 15:02 +0100, Frederic Weisbecker wrote:
> The possible usecase is so wide that I have a hard time to find a good > example. Counting instructions in exceptions on some specific syscalls, > counting instructions when some lock is taken on some irq handler, or > whatever...
All of which can be done without the recursion, but ok.
But what you're saying is that you want to be able to build a full expression tree of events.
Now the things I dislike about the whole thing is that its essentially a filter, and we already have a filter thing, this adds a second totally dis-joint filter capability.
Futhermore, you've split the start/stop things, as if they're somehow different, when in fact they're pretty much the same thing, and you can even think of more classes like a toggle event or whatever.
You've also split the start/stop events from the regular event lists making the whole event management and inheritance stuff even more complicated.
Furthermore, there is a definite possibility for weird behaviour in there, in that if you're trying to measure a similar event to the one that is used to enable/disable it, it very much depends on the order of the demux lists as to which is processed first.
The simply scheme I came up with is having these events be part of the event_group and add only one field:
pause_ops : 2
with:
enum perf_event_pause_ops { PERF_PAUSE_OP_NOP = 0, PERF_PAUSE_OP_INC, PERF_PAUSE_OP_DEC, PERF_PAUSE_OP_TOGGLE, };
and have INC increment the parent pause field and clip at INT_MAX, DEC decrement the pause field and clip at 0, and TOGGLE do ^1.
That however doesn't allow for these full expression trees, so we need to come up with something else. It does however do away with the ioctl()s, that redundant flag and the weird event separation.
It is still susceptible to the demux order.
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