* David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Ingo Molnar <mingo@xxxxxxx> > Date: Fri, 5 Dec 2008 08:03:29 +0100 > > > > > * Ingo Molnar <mingo@xxxxxxx> wrote: > > > > > This can be done in a very natural way with our abstraction, and the > > > "hello.c" example happens to do exactly that: > > > > multiple people pointed out that we have not posted hello.c :-/ > > Because it's completely not providing the facility. This is not how > people want to use the performance counters at all. > > And it doesn't even do what Paulus said is necessary, he said: > > -------------------- > > One thing that this sort of thing can't do is to get values from > > multiple counters that correlate with each other. For instance, we > > would often want to count, say, L2 cache misses and instructions > > completed at the same time, and be able to read both counters at very > > close to the same time, so that we can measure average L2 cache misses > > per instruction completed, which is useful. > -------------------- > > And if you read one counter then read the other as seperate operations, > you get extra events in there as a side effect of going back into > userspace between the two reads. that's wrong. If you _want_ to measure in a different context, with as little measurement impact as possible, you can do it with our code. The announcement provides the example for that. For example, i just started this bash infinite loop: $ while :; do :; done & [1] 1877 $ ./monitor -e 1 -c 1000000000 1877 IP: 0x00000031a2e70d4b IP: 0x0000000000455f64 IP: 0x00000031a2f028a0 IP: 0x0000000000440692 IP: 0x0000000000441b8e IP: 0x00000031a2e6f630 IP: 0x0000000000446129 IP: 0x00000031a2e6edbc IP: 0x0000000000443736 IP: 0x0000000000441c80 IP: 0x000000000043913a ^C We get IP readouts every 1 billion instructions executed in that shell. That shell is never stopped or otherwise intruded - it's kept as an as pristine of an execution environment as possible. Furthermore, the event readouts strictly only include event counts of the shell PID, _not_ of the monitor context's read() or other activities. > Nobody wants that, [...] Nobody wants that and we dont do it. Really, you should take a more serious look at our code. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
