cvs commit: src/sys/netinet tcp_syncache.c

[M. Warner Losh]

In message: <46575362.1050005 at freebsd.org>
            Andre Oppermann <andre at freebsd.org> writes:
: Robert Watson wrote:
: > 
: > On Fri, 25 May 2007, Andre Oppermann wrote:
: > 
: >>> Kernel-sourced log messages result in an fsync() of log files the 
: >>> message is written to, as syslogd feels that kernel messages are very 
: >>> important and should go to disk as quickly and reliably as possible.  
: >>> As a result, it's very desirable to rate limit (ideally no more than 
: >>> 1pps) packet-generated log messages.  I've been thinking of adding a 
: >>> spp function to match ppsprint for things like kernel warnings about 
: >>> the audit trail storage partition filling up, as one message a second 
: >>> is still a lot.
: >>
: >> kern.debug should not be automatically written and fsync()ed to disk. 
: >> All these TCP messages are sourced as kern.debug (except for the log_ 
: >> in_vain variety with kern.info but that's something the user has to 
: >> explicitly enable).
: > 
: > I don't know the actual historical reason, but I've always assumed that 
: > the fsync'ing of kernel log data is a result of kernel output being used 
: > for system debugging, which tends to occur when the system is behaving 
: > in an unstable way.  Syncing the messages to disk means that the chances 
: > of the message not being there later due to being lost somewhere in the 
: > cache are greatly reduced -- i.e., on a system crash, you want debugging 
: > data until the last possible moment.  I think this is useful behavior, 
: > although it does make klog a less useful logging mechanism for high 
: > volume debug data -- for that we generally prefer KTR + ALQ.
: 
: The syslog log level LOG_DEBUG is the lowest possible level and
: according to the descriptions meant to be used for informal messages
: during program debugging.  Everything below LOG_NOTICE should not
: need fsync after each line.  An examination of all users of LOG_DEBUG
: in our kernel doesn't show anything critical that would require fsync.
: The attached patch fixes syslog.conf in this regard.

/var/log/debug.log doesn't exist by default.  Also, this patch removes
*ALL* kernel messages from /var/log/messages, which isn't right
either.

Warner

: > My recommendation would simply be to stick this under pps and limit to 5 
: > warnings/sec or the like and stick with things basically as they are 
: > otherwise.  I would also suggest that these printfs be disabled in 
: > production systems, and solely used in the development branch (which is 
: > true now, but should remain true later).
: 
: OK, we can do that before 7.0R.
: 
: -- 
: Andre
: 
: $ cvs diff -up syslog.conf
: Index: syslog.conf
: ===================================================================
: RCS file: /home/ncvs/src/etc/syslog.conf,v
: retrieving revision 1.28
: diff -u -p -r1.28 syslog.conf
: --- syslog.conf 12 Mar 2005 12:31:16 -0000      1.28
: +++ syslog.conf 25 May 2007 21:20:54 -0000
: @@ -6,14 +6,15 @@
:   #      may want to use only tabs as field separators here.
:   #      Consult the syslog.conf(5) manpage.
:   *.err;kern.warning;auth.notice;mail.crit               /dev/console
: -*.notice;authpriv.none;kern.debug;lpr.info;mail.crit;news.err 
: /var/log/messages
: +*.notice;authpriv.none;lpr.info;mail.crit;news.err     /var/log/messages
:   security.*                                     /var/log/security
:   auth.info;authpriv.info                                /var/log/auth.log
:   mail.info                                      /var/log/maillog
:   lpr.info                                       /var/log/lpd-errs
:   ftp.info                                       /var/log/xferlog
:   cron.*                                         /var/log/cron
: -*.=debug                                       /var/log/debug.log
: +# do not call fsync() after each line for debug messages
: +*.=debug                                       -/var/log/debug.log
:   *.emerg                                                *
:   # uncomment this to log all writes to /dev/console to /var/log/console.log
:   #console.info                                  /var/log/console.log
: