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Re: performance problems



Hi,

In order to prevent syslogd from sync()'ing the disk on every write, you
can add a hyphen to the appropriate line, like this:
/etc/syslog.conf:
-------------------------------------------------------------------------
localmail.* 						-/var/log/maillog
-------------------------------------------------------------------------

Shachar.

On Tue, 24 Nov 1998, Peter L. Peres wrote:

> On Tue, 24 Nov 1998, Erez Doron wrote:
> 
> > Leandro Guimaraens Faria Corcete Dutra wrote:
> > > 
> > > Erez Doron wrote:
> > > >
> > > > > > because processes are starting and ending all the time,
> > > > >
> > > > >         You could run all these programs as daemons from the
> > > > >
> > > > all thease programs are daemons, which ran from inetd !
> > > > ( like pop, ftp,telnet etc...) i can not run them from /etc/rc...
> > > 
> > >         Well then, they are not starting and stopping all the time!  Daemons
> > > may fork now and then according to load, but they will neither start nor
> > 
> > inetd forking and then execve ipop3d, is same as starting ipop3d !
> > 
> > > stop unless the machine reboots or the superuser kills them.
> > > 
> > >         Have you tried already running top in a small window and checking which
> > > process is "eating" you CPU away when the cursor halts?  I think I have
> > 
> > well, both cpus are below 10% usage, so no process is eating my cpu
> > 
> > but I think that the problem is syslogd, which does not write to
> > cache, but directly to disk, so if it has somthing to write, it freezes
> > the system untill it's done.
> > 
> > i soved the problem by killing syslogd, but that's not a good idea
> > > no other ideas...
> 
> Here is one: mount a ramdisk and arrange for syslogd to write there. You
> will have to be careful not to fill the partition (only 4M w/o hacks). 
> This is MUCH faster than HDD. You can mirror it to HDD once in a while
> using a cron script or a small program. The other idea is to stripe the
> /var/adm so it's on a different drive than most other things. The third
> idea is to make syslogd log on another machine ONLY (see syslog.conf). 
> 
> There are also other performance tuning issues for machines that run a
> lot of processes, such as slowing down the task swapper in the kernel and
> changing the swapper and cache buffer page policy. These cannot be done
> easily by a user/sysadmin (I think you can choose the swapper policy at
> compile time by selecting 'optimize as server' in make config - but don't 
> take my word for it). There is more to be done, such as setting the
> interrupt priorities differently and looking into real time Linux, which
> can guarantee latencies to some extent.
> 
> Erez, you must be one of the few people in the world who are stressing
> Linux to the limit all the time ;) No-one that I know runs a production
> network from a machine that is used as an X terminal/server at the same
> time ;) And I think that it's funny that the only complaint is, slow
> cursor response in X (which may be due to the mouse interrupt having a low
> priority vs. disk and ether).
> 
> Peter
> 
> 

Shachar Tal
-------------
Taub Computer Center, Technion, Israel Institute of Technology
finger me for contact info or PGP key.

`When you say "I wrote a program that crashed Windows", people just stare
at you blankly and say  "Hey, I got those with the system,  *for free*".'
                                                         (Linus Torvalds)