[Pki-devel] [PATCH] 4 Replaced byte-to-char & char-to-byte converters.

[Ade Lee]

On Wed, 2011-12-21 at 12:31 -0800, Andrew Wnuk wrote:
> On 12/21/2011 11:23 AM, Ade Lee wrote:
> >
> >>> If there is an unacceptable degradation in performance, perhaps we could
> >>> utilize some customized Java classes to perform these functions. As an
> >>> alternative approach, as Endi alluded to, there is some ASN.1 code in
> >>> Mozilla JSS, and speaking with Bob Relyea, we have been postulating on
> >>> how much work would be involved to write JNI bindings via JSS to the
> >>> ASN.1 encoders/decoders contained in NSS instead of moving this code to
> >>> use java.nio.* classes. Theoretically, we may limit our performance
> >>> issues in exchange for the extra work involved in making the effort to
> >>> standardize on the NSS ASN.1 engine (although I don't know if this will
> >>> resolve issues such as (3) noted above).
> >>
> >> I checked the code, it looks like some of Mozilla's JSS code also relies
> >> on the Charset API. JNI calls have some overhead too, so we need to know
> >> how it's going to be used to avoid negative performance impact.
> >>
> >
> > I agree the performance is a concern, and is something that we should
> > keep in mind, but it is not clear that differences in performance in
> > these classes will degrade the performance of the system.  The only way
> > to determine where the system is really spending its time is by running
> > it through a profiler and analyzing the results.  We may find that the
> > server spends comparatively no time in this code.
> 
> I think "may" is a proper keyword here.  If someone, calls "Charset API" 
> a "bottleneck" that should be good enough warning to do some simple 
> testing to verify it.
> 
Lets say we do a simple test and the encoding takes 3 ms instead of 1 ms
to complete.  What then?  Do we reject the patch?  Do we embark on a
process whereby we investigate custom code or look into JSS functions?  

No - we do not.  Why?  Because we have no idea whether this is even a
bottleneck for our server.  Just because it was a bottleneck for someone
else for some random app - does not mean it will be the same for us.  It
may end up being a huge bottleneck - or it may be completely irrelevant.
We do not know - and we will not know - until we do profiling.

Without profiling information, we are optimizing in the dark, and we
will very likely spend a lot of wasted time optimizing the wrong things.

> >
> >
> > On the other hand, we have a compelling reason to change these classes.
> > The classes are deprecated - and will go away - and then everything will
> > stop working.
> >
> > I suggest that we review this patch for correctness.
> 
> I think Matt's email was clear. This patch is fine but we had 3 concerns 
> which were listed in his email.
> 
> >    Is the encoding
> > correct?
> 
> There is no simple test to prove this or to replace years of 
> compatibility testing (case like (3) can be good example of this).
> 
> >    Do the unit tests cover enough - or have the right inputs to
> > validate the correctness of the conversion?  It seems like there were
> > situations like (3) where perhaps more testing is required.
> 
> Agreed, there was always apparent reason for fixes like (3).
> 
> >
> >
> > And we should schedule a performance testing and profiling task for next
> > year.  We will always have the 8.x code as a benchmark.  If at that
> > time, we find that these classes cause performance problems, we can
> > always look into custom classes or maybe JSS code.
> >
> > It seems to me that talking about custom classes before having any
> > profiling data is putting the cart before the horse.
> >
> > Ade
> >
> >
>