Messages in this thread |  | | Subject | Re: [Lse-tech] Re: (RFC): SKB Initialization | Date | Fri, 23 Aug 2002 13:51:05 -0700 | From | Rick Lindsley <> |
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Read the 1st email. There were 2.4 million samples.
How many do you think is sufficient ?
I looked at my hand 2.4 million times and it was not wet each time. Therefore, it is not raining.
Of course, if I am inside a roofed structure, the sampling is faulty. And (correct me if I'm wrong here, Dave) I think that's what we're asking about. Are the samples you're getting pertinent and significant? If, as you suggested in another email, you disable interrupts in the functions to take these measurements, you may be significantly altering the very environment you hope to measure.
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.
That will be helpful. Microbenchmarks which measure cycles are far less interesting to the community than the end results of actual workloads. Note that Mala said "I measured the cycles for only the initialization code in alloc_skb and __kfree_skb" which could mean that even other parts of alloc_skb() or __kfree_skb() may have gotten worse and you would not have known. Later she admits, "As the scope of the code measured widens the percentage improvement comes down" and finally observes "We measured it in a web serving workload and found that we get 0.7% improvement" which is practically in the noise. Dave's observation was that it was slightly worse (0.35%). Either could be statistical noise. If the patch only creates statistical noise, the community won't be interested.
Also, it is well known and widely recognized that more cpus add increasing complexity with cache and code interactions. Have you tested this on an 8-way machine, rather than a 2-way, and do the results still hold? Things which look very good on 2-proc can start to lose their lustre on 8-proc or bigger.
I'm unfamiliar with netperf -- does it yield "results" which can be compared? If so, since it was used to generate the load, how did the results of the two runs compare?
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