On 3/25/2013 8:01 PM, Vladimir Panteleev wrote:
On Tuesday, 26 March 2013 at 02:57:07 UTC, Walter Bright wrote:
While you can get the caller (after all, debuggers do it), it can be
arbitrarily costly (in terms of execution speed) to do so, which can negate
many of the advantages of a probing profiler.
What? You just read the value EBP is pointing at, or something like that.
Walking the call stack is basically walking a linked list.
If only it were that simple.
1. many stack frames do not have an EBP
2. the stack frames on Win64 require doing a bunch of table searches to figure
out - they don't use EBP
3. even when you find the return address, then it's a costly process to figure
out what function that address belongs in
The ones I've seen didn't bother to do it.
Maybe they just weren't very good profilers ;) I've tried a few before I found
Very Sleepy.
Fan in/out is very useful because the most effective optimization is to not
call the time consuming functions, and this path information enables you to
figure out where you don't really need to call it.
Who's arguing that?
Just wanted to point out how useful it is!
