Date: Fri, 31 Jul 1998 13:59:56 -0700 (PDT) From: Craig Spannring <cts@internetcds.com> To: chanders@timing.com (Craig Anderson) Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Using FreeBSD for data acquisition? (long) Message-ID: <199807312059.NAA18156@bangkok.office.cdsnet.net> In-Reply-To: <199807311853.MAA04187@count.timing.com> References: <199807311853.MAA04187@count.timing.com>
next in thread | previous in thread | raw e-mail | index | archive | help
That pretty much matches what I'm seeing for a server I'm writing.
My server must respond in less than 3 seconds. Normally it is able
to respond in a millisecond or two, but occasionally it takes around
1000 milliseconds.
I've duplicated the problem occurring even under real time priority
with no other processes on the machine except for init, pagedaemon,
vmdaemon, update, and one csh. I had virtual memory disabled to
eliminate any paging activity.
I tracked the problem down to the fact that I'm not getting any CPU
time for a substantial (at least up to 500 milliseconds) amount of
time even though I'm using rtprio and there is nothing else that
should be running.
For years I've said that Unix is not a RTOS. For my application I
think I can get by with FreeBSD. Your application sounds like it is
more critical RT and I would recommend you go with a RTOS.
In regards to your question of why 0.100 seconds is so common, FreeBSD
uses a 10msec quantum. I suspect if you change kern.quantum to some
other value then the other value will become more common.
Let me know if you find some way that helps the latency.
--
=======================================================================
Life is short. | Craig Spannring
Ski hard, Bike fast. | cts@internetcds.com
--------------------------------+------------------------------------
Any sufficiently perverted technology is indistinguishable from Perl.
=======================================================================
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199807312059.NAA18156>