lkml.org 
[lkml]   [2009]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4] ftrace - add function_duration tracer
Hi -


On Thu, Dec 10, 2009 at 07:35:08PM +0100, Ingo Molnar wrote:
> [...]
> target_set.stp is not really adequate. Have you actually _tried_ to use
> it on something real like hackbench, which runs thousands (or tens of
> thousands) of tasks? You'll soon find that associative arrays are not
> really adequate for that ... [...]

A few thousand entries in a hash table is really not that big a deal.


> > > Also, i dont think stap supports proper separation of per workload
> > > measurements either. I.e. can you write a script that will work
> > > properly even if multiple monitoring tools are running, each trying
> > > to measure latencies?
> >
> > Sure, always has. You can run many scripts concurrently, each with
> > its own internal state. (Overheads accumulate, sadly & naturally.)
>
> To measure latencies you need two probes, a start and a stop one. How do
> you define a local variable that is visible to those two probes? You
> have to create a global variable - but that will/can clash with other
> instances.

You misunderstand systemtap "global" values. They are global to that
particular execution of that particular script. They are not shared
between scripts that may be concurrently running.


> ( Also, you dont offer per application channels/state from the same
> script. Each app has to define their own probes, duplicating the
> script and increasing probe chaining overhead. )

Please elaborate what you mean.


> > > Also, i personally find built-in kernel functionality more trustable
> > > than dynamically built stap kernel modules that get inserted.
> >
> > I understand. In the absence of a suitable bytecode engine in the
> > kernel, this was the only practical way to do everything we needed.
>
> You seem to be under the mistaken assumption that your course of action
> with SystemTap is somehow limited by what is available (or not) in the
> upstream kernel. In reality you can implement anything you want [...]

The message we have received time, after time, after time was
stronger: that a suitable interpreter was not going to be welcome in
tree. If this is relaxed (and perhaps even if not), we may prototype
such a thing in the new year.


- FChE


\
 
 \ /
  Last update: 2009-12-10 19:53    [W:3.081 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site