On Sep 22, 11:51 am, Mikhail Naganov <[email protected]> wrote:
> Hi Andy,
>
> What Erik said is absolutely correct. Theprofilerdoes sampling, and
> if it sees samples that can't be attributed to JS code (that is,
> rendering, DOM, etc.), it accounts them to '(program)' entry.
>
> If your web app's most weight is in '(program)' entry, this means that
> your JS code just isn't heavy enough, in other words, your hot spot
> isn't on JS side. What to do in this case? You can try to use another
> tool, like "Page speed" (http://googlecode.blogspot.com/2009/06/
> introducing-page-speed.html) to get some insights.
OK, I see. But then I have to ask why it has to be a sampling
profiler. An instrumented profiler will reveal the time spent outside
of JS code (but still called from JS code).
The reason is that if I my bottleneck is DOM manipulation, then to fix
it, I need it to be attributed to some JS code! After all, the only
thing I can change is JS code. I can't speed up Chrome as an
application writer, and that is besides the point because we're
writing cross-browser JS code. Often I have a bunch of third party
code, and I don't even know what kind of DOM manipulation it's doing.
I think this is a rather severe problem. Have you seen lots of real
JS apps that spend most of their time strictly in the JS interpreter?
I used it on Gmail, and although I'm not a Gmail developer, it doesn't
seem very useful (aside from the obfuscated function names), as 90% of
the time is an opaque block.
As a more concrete example, if some JS code is making 100,000 calls to
some expensive function, say document.getElementById('foo'), then the
profiler should show me this block under the function that called it,
rather than lumping it in with the rest of the time spend rendering
images, etc. Maybe I will cook up a test of this to show the problem.
Andy
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