[Interest] update on building Qt/Linux with clang?

[René J. V. Bertin]

Thiago Macieira wrote:


> More importantly, the decompression times: gzip took 0.84s, zstd 0.30s and xz
> 2.81s. But bzip2 needed 6.6s.

I cannot reproduce those relative performance figures on neither of my machines. 
On a 95Mb directory I'm getting on my Mac (tar -c dir | $compressor $opts > 
/dev/null):
xz -c6: 40.2s (100%)
xz -c6 --threads=4: 16.3s (362%)
bzip2 -9: 10.3s (100%)
pbzip2 -9: 5s (392%)

Similar relative figures on my much slower Linux machine.

Interestingly parallelisation incurs about a 50% overhead on Mac. Also, pxz/xz 
--threads=N doesn't always give a performance gain, either because of the input 
size I'm testing with, or because I'm compressing stdin. I don't really want to 
spend more time figuring that out.

> negligible < significant < considerable

Nope, something can be highly significant but perfectly negligible.

> I'm claiming that the size is less than what you claim to be a problem.

Who said anything about problems? I'm talking about trade-offs.

> That's why you should strip them out and compress them. Store them where you
> may need them (possibly never).

I need to be able to get useful post-mortem backtraces, and typically don't want 
to have to figure out which debug information to get back online and how. That's 
part of the trade-off. On my faster/bigger system I build all of Qt with 
embedded debug info, elsewhere I only add debug info to QtBase.

R.