Messages in this thread |  | | Date | Fri, 23 Aug 2002 09:39:13 -0700 | From | Dave Hansen <> | Subject | Re: [Lse-tech] Re: (RFC): SKB Initialization |
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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.
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?
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.
http://www.sr71.net/~specweb99/old/run-specweb-2300-nodynpost-2.5.31-bk+profilers-08-14-2002-02.19.22/callgraph
The end result, as I can see it, is that your patches hurt Specweb performance. They moved the profile around, but there was an overall decline in performance. They partly address the symptom, but not the real problem. We don't need to _tune_ it, we need to fix it.
The e1000's need to allocate/free fewer skbs. NAPI's polling mode _should_ help this, or at least make it possible to batch them up. -- Dave Hansen haveblue@us.ibm.com
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