Re: stomping static data pull

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
> On Thursday 2009-10-29 16:59, Patrick McHardy wrote:
>>> On Wednesday 2009-10-28 16:57, Patrick McHardy wrote:
>>>> Jan Engelhardt wrote:
>>>>> I incorporated your suggestions and propose this new 4-series set.
>>>> Could you give me a short description of the changes relative
>>>> to the first incarnation? Thanks.
>>> http://osdir.com/ml/general/2009-08/msg10540.html
>>> - splitting xt_repldata_create
>>> - giving it a name of your choice
>>> - return semantics (found a missing return keyword; just refreshed top 
>>> is commit v2.6.32-rc3-4-g7891b6c)
>>>
>> OK thanks, that leaves my worries about adding additional runtime
>> overhead. I'll do some quick benchmarks to see if it really has
>> a measurable impact.
>>
> How would one measure this in a meaningful way? rdtsc? (that would only 
> work on x86, in fact.)
> 
> And I guess that one could 
> always construct a case whereby the patched result looks 'slow'. :/

Sure .. but I don't think it will matter much in comparision to large
rulesets. I usually use get_cycles() in nf_hook_slow() to calculate
the cycles spent in the netfilter hook functions. In this case just
measuring the difference before and after with all affected tables
loaded, but without any rules, seems fine to me.