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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