By Darryl Gove-Oracle on Nov 11, 2014
I love using the Performance Analyzer, but the question I often get when I show it to people, is "Where do I start?". So one of the improvements in Solaris Studio 12.4 is an Overview screen to help people get started with the tool. Here's what it looks like:
The reason this is important, is that many applications spend time in various place - like waiting on disk, or in user locks - and it's not always obvious where is going to be the most effective place to look for performance gains.
The Overview screen is meant to be the "one-stop" place where people can find out what their application is doing. When we put it back into the product I expected it to be the screen that I glanced at then never went back to. I was most surprised when this turned out not to be the case.
During performance analysis, I'm often exploring different ideas as to where it might be possible to get performance improvements. The Overview screen allows me to select the metrics that I'm interested in, then take a look at the resulting profiles. So I might start with system time, and just enable the system time metrics. Once I'm done with that, I might move on to user time, and select those metrics. So what was surprising about the Overview screen was how often I returned to it to change the metrics I was using.
So what does the screen contain? The overview shows all the available metrics. The bars indicate which metrics contribute the most time. So it's easy to pick (and explore) the metrics that contribute the most time.
If the profile contains performance counter metrics, then those also appear. If the counters include instructions and cycles, then the synthetic CPI/IPC metrics are also available. The Overview screen is really useful for hardware counter metrics.
I use performance counters in a couple of ways: to confirm a hypothesis about performance or to estimate time spent on a type of event. For example, if I think a load is taking a lot of time due to TLB misses, then profiling on the TLB miss performance counter will tell me whether that load has a lot of misses or not. Alternatively, if I've got TLB miss counter data, then I can scale this by the cost per TLB miss, and get an estimate of the total runtime lost to TLB misses.
Where the Overview screen comes into this is that I will often want to minimise the number of columns of data that are shown (to fit everything onto my monitor), but sometimes I want to quickly enable a counter to see whether that event happens at the bit of code where I'm looking. Hence I end up flipping to the Overview screen and then returning to the code.
So what I thought would be a nice feature, actually became pretty central to my work-flow.
I should have a more detailed paper about the Overview screen up on OTN soon.