On Tue, Sep 13, 2016 at 10:18 PM, Josh Poimboeuf [off-list ref] wrote:

On Tue, Sep 13, 2016 at 06:45:00PM +0900, Byungchul Park wrote:

quoted

Currently, x86 implementation of save_stack_trace() is walking all stack
region word by word regardless of what the trace->max_entries is.
However, it's unnecessary to walk after already fulfilling caller's
requirement, say, if trace->nr_entries >= trace->max_entries is true.

I measured its overhead and printed its difference of sched_clock() with
my QEMU x86 machine. The latency was improved over 70% when
trace->max_entries = 5.

This code will (probably) be obsoleted soon with my new unwinder.

Hello,

You are right.

I also think this will probably be obsoleted with yours.
So I didn't modify any details of the patch.
I will take your comment into account if it becomes necessary.

Anyway, crossrelease needs this patch to work smoothly.
That's only reason why I included this patch in the thread.

Thank you,
Byungchul

Also, my previous comment was ignored:

  Instead of adding a new callback, why not just check the ops->address()
  return value?  It already returns an error if the array is full.

  I think that would be cleaner and would help prevent more callback
  sprawl.

--
Josh

-- 
Thanks,
Byungchul

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