Date: Fri, 25 May 2007 16:58:23 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: andre@freebsd.org Cc: cvs-src@freebsd.org, glebius@freebsd.org, rwatson@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/netinet tcp_syncache.c Message-ID: <20070525.165823.29499700.imp@bsdimp.com> In-Reply-To: <46575362.1050005@freebsd.org> References: <46569762.6090801@freebsd.org> <20070525090951.F53865@fledge.watson.org> <46575362.1050005@freebsd.org>
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In message: <46575362.1050005@freebsd.org>
Andre Oppermann <andre@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
:
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