Re: [Lse-tech] Re: (RFC): SKB Initialization

From: Bill Hartner (
Date: Fri Aug 23 2002 - 15:12:40 EST

Dave Hansen wrote:
> Mala Anand wrote:
> > Readprofile ticks are not as accurate as the cycles I measured.
> > Moreover readprofile can give misleading information as it profiles
> > on timer interrupts. The alloc_skb and __kfree_skb call memory
> > management routines and interrupts are disabled in many parts of that code.
> > So I don't trust the readprofile data.
> I don't believe your results to be accurate. They may be _precise_
> for a small case, but you couldn't have been measuring them for very
> long. A claim of accuracy requires a large number of samples, which
> you apparently did not do.


What is your definition of a "very long time" ?

Read the 1st email. There were 2.4 million samples.

How many do you think is sufficient ?

> I can't use oprofile or other NMI-based profilers on my hardware, so
> we'll just have to guess. Is there any chance that you have access to
> a large Specweb setup on hardware that is close to mine and can run
> oprofile?

Why do you think oprofile is a better way to measure this ?
BTW, Mala works with Troy Wilson who is running SPECweb99 on
an 8-way system using Apache. Troy has run with Mala's patch
and that data will be posted.

> Where are interrupts disabled? I just went through a set of kernprof
> data and traced up the call graph. In the most common __kfree_skb
> case, I do not believe that it has interupts disabled. I could be
> wrong, but I didn't see it.

What is the revelance of the above ?

> The end result, as I can see it, is that your patches hurt Specweb
> performance.

Based on what ? A callgraph ? A profile ?

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This archive was generated by hypermail 2b29 : Fri Aug 23 2002 - 22:00:29 EST