[TUHS] MacOS X is Unix (tm)

Larry McVoy lm at mcvoy.com
Wed Jan 4 04:20:54 AEST 2017


On Tue, Jan 03, 2017 at 02:17:00PM +0100, Joerg Schilling wrote:
> Larry McVoy <lm at mcvoy.com> wrote:
> 
> > I'd like to know where you can get a better performing OS.  The file systems
> > scream when compared to Windows or MacOS, they know about SSDs and do the
> > right thing.  The processes are light weight, I regularly do "make -j"
> > which on my machines just spawns as many processs as needed.
> ...
> 
> > So if I size it to the number of CPUs it is slightly faster.  On the other
> > hand, when I tell it just spawn as many as it wants it peaks at about 267
> > processes running in parallel.
> >
> > Solaris, AIX, IRIX, HP-UX, MacOS would all thrash like crazy under that 
> > load, their context switch times are crappy.
> >
> > Source: author of LMbench which has been measuring this stuff since the
> > mid 1990s.
> 
> Could you give a verification for this claim please?

First, it was two claims, fast file system, and fast processes.  You 
seem to have ignored the second one.  That second one is a big deal 
for multi process/multi processor jobs.

If you have access to solaris and linux running on the same hardware, 
get a copy of lmbench and run it.  I can walk you through the results
and if LMbench has bit rotted I'll fix it.

http://mcvoy.com/lm/bitmover/lmbench/lmbench2.tar.gz

> >From what I can tell, the filesystem concepts in Linux are slow and it is 
> usually not possible to tell what happened in a given time frame. It however
> creates the impression that it is fast if you are the only user on a system,
> but it makes it hard to gauge a time that is comparable to a time retrived 
> from a different OS. This is because you usually don't know what happened in
> a given time.

You are right that Linux has struggled under some multi user loads (but then
so does Netapp and a lot of other vendors whose job it is to serve up files).

There are things you can do to make it faster.  We used to have thousands 
of clones of the linux kernel and we absolutely KILLED performance by walking
all those and hardlinking the files that were the same (BitKeeper, unlike
Git, has a history file for each user file so lots of them are the same 
across different clones).

The reason it killed performance is that Linux, like any reasonable OS,
will put files next to each other.  If you unpack /usr/include/*.h
it is very likely that they are on the same cylinder[s].  When you start
hardlinking you break that locality and reading back and one directory's
set of files is going to force a lot of seeks.

So don't do that.

Another thing that Linux [used to have] has is an fsync problem, an fsync
on any file in any file system caused the ENTIRE cache to be flushed.  
I dunno if they have fixed that, I suspect so.

My experience is that for a developer, Linux just crushes the performance
found on any other system.  My typical test is to get two boxes and time

$ cd /usr && time tar cf - . | rsh other_box "cd /tmp && time tar xf -; rm -rf
/tmp/usr"

I suspect your test would be more like

$ cat > /tmp/SH <<EOF
cd /
for i in *
do	test -d $i || continue
	tar cf /tmp/$i.tar $i &
done
wait
EOF
$ time sh /tmp/SH

and it may very well be that Linux doesn't do that well (though I doubt it
because that's essentially what bkbits.net [our github] was doing and a
dual processor 1ghz athlon with one spinning disk was happily serving up
a bizillion clones of the linux kernel and a lot of other stuff).



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