From owner-freebsd-stable Mon Mar 1 18:45:24 1999 Delivered-To: freebsd-stable@freebsd.org Received: from mail.HiWAAY.net (fly.HiWAAY.net [208.147.154.56]) by hub.freebsd.org (Postfix) with ESMTP id B6C4515472 for ; Mon, 1 Mar 1999 18:45:13 -0800 (PST) (envelope-from dkelly@nospam.hiwaay.net) Received: from nospam.hiwaay.net (tnt8-216-180-15-244.dialup.HiWAAY.net [216.180.15.244]) by mail.HiWAAY.net (8.9.1a/8.9.0) with ESMTP id UAA09760; Mon, 1 Mar 1999 20:44:54 -0600 (CST) Received: from nospam.hiwaay.net (localhost [127.0.0.1]) by nospam.hiwaay.net (8.9.2/8.9.2) with ESMTP id UAA02047; Mon, 1 Mar 1999 20:44:51 -0600 (CST) (envelope-from dkelly@nospam.hiwaay.net) Message-Id: <199903020244.UAA02047@nospam.hiwaay.net> X-Mailer: exmh version 2.0.2 2/24/98 To: Andrew McNaughton Cc: freebsd-stable@FreeBSD.ORG From: David Kelly Subject: Re: rc5des slows tape thruput In-reply-to: Message from Andrew McNaughton of "Mon, 01 Mar 1999 19:03:40 +1300." <199903010603.TAA09311@aniwa.sky> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Mon, 01 Mar 1999 20:44:51 -0600 Sender: owner-freebsd-stable@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Andrew McNaughton writes: > > Does the tape process get niced also then? No. > Is the nice setting reasonable? Yes. > If not then why is rc5des allowed to slow it so much? The picture that I'm getting is a single block is written to the tape drive at a time. When the tape drive is ready for another block rc5des's current time slice is not aborted but allowed to complete before dd gets a time slice to queue another block to the tape. The drive at home has 1M of internal RAM, the DDS-3 drives at work have 2M buffers. It would appear FreeBSD doesn't make use of these buffers. > I don't imagine that dd to tape would need that much CPU. I'd expect > it to bottleneck on IO. Is it something to do with needing very small > chunks of CPU t ime and running into lots of small waits for the > kernel's CPU time allocation? A couple of percent. Using dd to read /dev/zero and write /dev/null yields 208M/sec w/o rc5des running, 203M/sec with, writing 100000 blocks of 10k (roughly 1G) so the test runs long enough to be valid. -- David Kelly N4HHE, dkelly@nospam.hiwaay.net ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message