Re: [Caml-list] gc overhead

[Peter Hawkins <hawkinsp@cs.stanford.edu>]

Hi...

On Tue, Mar 2, 2010 at 12:11 PM, Warren Harris <warrensomebody@gmail.com> wrote:
>
> On Mar 1, 2010, at 12:54 AM, Richard Jones wrote:
>
>> On Sun, Feb 28, 2010 at 04:16:03PM -0800, Warren Harris wrote:
>>>
>>> I would like to determine what percentage of my application's cpu time
>>> is spent in the garbage collector (for tuning purposes, but also just
>>> to monitor the overhead). Is there any way to obtain this information
>>> short of using gprof? Additional information provided by Gc.stat would
>>> be ideal, or perhaps a Gc.alarm that was called at the beginning of
>>> the gc cycle, but neither of these seem to exist.
>>
>> I would have to say what's wrong with using gprof?
>
> What's wrong with it is that it provides no way to monitor gc overhead in an
> active service.

I would have recommended using oprofile on linux, which I greatly
prefer to GCC's built-in profiling support for profiling C programs.
It has a low and tunable overhead, and because it's a sampling
profiler it doesn't perturb the results anywhere near as much as
standard profiling instrumentation.

Unfortunately last time I checked it had poor OCaml support (no
support for unwinding the OCaml call stack, so no context-sensitivity
in the profiles). That said, you probably don't need
context-sensitivity to determine the fraction of execution time spent
in the GC.

It might be worth a try...

Peter