[devel] [PATCH 0/3] optimize rpmsetcmp()

[Alexey Tourbin]

On Sun, Dec 05, 2010 at 03:03:16AM +0300, Dmitry V. Levin wrote:
> > > apt-rpm indeed calls rpmRangesOverlap() too many times, it's common
> > > knowledge.  Unfortunately, stating this fact isn't sufficient to make
> > > apt-rpm work faster.
> > 
> > So what do you think?  There's a possibility to change bitv[] to bitmap,
> > per Kirill's proposal.  That mighit yield about, say 30% user time cutdown.
> 
> 30% is a bit optimistic, according to my measurements.
> 
> > However, note that apt is not only eager for user time.  System time is
> > being spent with splendor as well.
> 
> System time takes only about 15% of elapsed time, according to my
> measurements.

Under VirtualBox, which seems to become a common hardware nowadays,
system time is somewhat more noticable.

> > Personally, I like bitv[], and I don't like something like <sys/select.h> stuff.
> 
> When performance is the issue, there should be a good rationale to choose
> the approach that works slower.

There are other reasons, such as keeping the code comprehensible (at the
expense of some runtime penalties).  I think the concept of bitv[] is
crucial for understanding the code, and it helps to keep the code clean
and self-evident.  Replacing bitv[] with bitmap might be a major trade-off
for the sake of performance.  Or might not.