From owner-freebsd-hackers Tue Feb 23 0:52:59 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from herring.nlsystems.com (nlsys.demon.co.uk [158.152.125.33]) by hub.freebsd.org (Postfix) with ESMTP id 610E611694 for ; Tue, 23 Feb 1999 00:52:54 -0800 (PST) (envelope-from dfr@nlsystems.com) Received: from localhost (dfr@localhost) by herring.nlsystems.com (8.9.3/8.8.8) with ESMTP id IAA60504; Tue, 23 Feb 1999 08:50:57 GMT (envelope-from dfr@nlsystems.com) Date: Tue, 23 Feb 1999 08:50:57 +0000 (GMT) From: Doug Rabson To: Julian Elischer Cc: Don Lewis , Terry Lambert , Matthew Dillon , freebsd-hackers@FreeBSD.ORG Subject: Re: Panic in FFS/4.0 as of yesterday In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Mon, 22 Feb 1999, Julian Elischer wrote: > softupdates already "kinda" doesn this.. > it queues data writes at one point in the future and directory writes > at a different point in the future. I believe that data writes must be > completed before inode writes which must be completed before directory > writes. If they are not the the dependencies will FORCE that ordering. > > The reason to preschedule the different actions is to make it all happen > in the right order anyhow, so that the dependency tracking is a big NOP. I think softupdates will be less affected by this but there can still be problems with latency. The time for a simple directory read (not a softupdate controlled operation) can be delayed significantly since it gets queued behind all the rest of the async i/o. In Matt's test, I saw about 5Mb queued at one point which translates to a latency of over 0.5sec, assuming the drive throughput is about 8Mb/sec. -- Doug Rabson Mail: dfr@nlsystems.com Nonlinear Systems Ltd. Phone: +44 181 442 9037 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message