Date: Tue, 23 Feb 1999 08:50:57 +0000 (GMT) From: Doug Rabson <dfr@nlsystems.com> To: Julian Elischer <julian@whistle.com> Cc: Don Lewis <Don.Lewis@tsc.tdk.com>, Terry Lambert <tlambert@primenet.com>, Matthew Dillon <dillon@apollo.backplane.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Panic in FFS/4.0 as of yesterday Message-ID: <Pine.BSF.4.05.9902230847020.60339-100000@herring.nlsystems.com> In-Reply-To: <Pine.BSF.3.95.990222114340.7463A-100000@current1.whistle.com>
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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
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