Re: [PATCH v3 01/15] x86/dumpstack: Optimize save_stack_trace

[Josh Poimboeuf]

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

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