[TUHS] MacOS X is Unix (tm)

Joerg Schilling schily at schily.net
Tue Jan 3 23:17:00 AEST 2017


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?

My experiences are different.

>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.

If you e.g. use gtar to unpack a Linux kernel archive on your local disk, the 
wall clock run time of gtar is low, but it takes some time before the first 
disk I/O takes place and the disk I/O continues until a long time after gtar 
already returned control to the shell.

If you however use star for the same task and do not specify the "-no-fsync" 
option, star takes 4x longer than gtar to return control to the shell. If you
do the same on Solaris using the same hardware, a standard star extract (with 
the default fsync) takes only 10% more real time with UFS compared to the time
without fsync and the time is aprox. the same as the unpack time on Linux 
using gtar. This is because on Solaris, disk I/O starts immediately even when 
you use gtar and there is no time wasted with filling the kernel cache before 
I/O starts.

Aprox. 12 years ago, I converted the central web server for the OSS hosting 
platform berlios.de (*) (at that time the second largest one) from Linux to 
Solaris and the performance did increase ponderably.... Even worse, at the 
same time, I did a test where I unpacked the Linux kernel archive using gtar
and switched off the power just after gtar returned control to the shell. The 
result was a rotten filesystem that could not be repaired by fsck.

***
So my question is: did you manage to find a method to gauge something 
on Linux that is comparable to other platforms or do you also suffer from the
problem that Linux tries to hide the real time needed for filesystem 
operations?
***

BTW: ZFS has a similar problem as Linux: It is extremely slow when you ask it 
to to things in a way that result in a known state. ZFS however does not result 
in a rotten FS when you switch the system off while it is updating the FS.


*) The reason for this conversion was that Linux completely stalled 3-4 times a 
day and only a reset did help. There was no way to get the reason for that 
problem using Linux debug tools. After the conversion to Solaris, it turned out 
that memory overcommitment on Linux was the reason for the freeze. Since we had 
two CPUs, the Linux kernel could copy on write pages faster than searching for 
processes to kill in order to recover.



Jörg

-- 
 EMail:joerg at schily.net                  (home) Jörg Schilling D-13353 Berlin
       joerg.schilling at fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
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