Date: Tue, 08 Apr 2003 23:09:17 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Ollivier Robert <roberto@keltia.freenix.fr> Cc: Dag-Erling Smorgrav <des@ofug.org> Subject: Re: cvs commit: src/sys/dev/ata ata-all.c ata-all.h ata-chipset.cata-dma.c ata-pci.c ata-pci.h Message-ID: <25388.1049836157@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 08 Apr 2003 22:23:08 %2B0200." <20030408202308.GA49094@tara.freenix.org>
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In message <20030408202308.GA49094@tara.freenix.org>, Ollivier Robert writes: >According to Poul-Henning Kamp: >> Tagged queueing: >> Ability to reduce transaction latency by sending more than one >> request to the drive at a time. The request may be handled out >> of order by the drive. >> (A good thing!) > >Except for softupdates which rely on its own ordering of writes... This actually has nothing to do with it. If the drive only replies to the transaction when the data is actually written, the biodone() will reach softupdates and the right thing happen. Soft updates does not really care if I/O transactions are reordered, but it cares a lot about being able to trust that they are actually written to stable storage, not just some cache, when drivers say so. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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