Date: Tue, 7 Dec 1999 14:09:28 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Mike Smith <msmith@FreeBSD.ORG> Cc: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern kern_shutdown.c Message-ID: <199912072209.OAA31610@apollo.backplane.com> References: <199912071824.KAA02863@mass.cdrom.com>
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:> It only issues writes for buffers that can be written out of order,
:> then waits for the SCSI command to complete before issuing the
:> dependancies.
:
:It'd be interesting to elide the wait and see if this improved
:throughput. It's not (really) much of a safeguard once you assume that
:disks/downstream caches are write-buffering things anyway.
:
:(Making that behaviour default would not be a good idea, but it'd be
: interesting to see what impact it might have.)
It would have no impact at all. Softupdates is an asynchronous
mechanism and it is able to parallelize I/O significantly -- for
example, it is fully able to commit 10 data blocks simultaniously,
it is simply that it will not commit the indirect block elements pointing
to those data blocks (recursively) until the data block commit has
completed.
I do not assume that disks/downstream caches are returning completion
on the SCSI request prior to the physical write to the media
(or other non-volatile storage) completing. This is totally unrelated
to using ordered or unordered tags.
-Matt
Matthew Dillon
<dillon@backplane.com>
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