Messages in this thread | | | Date | Mon, 28 Jun 1999 13:16:47 -0700 (PDT) | From | Matthew Jacob <> | Subject | Re: direct (unbufferd) disk access |
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> > On Mon, 28 Jun 1999 09:24:06 -0700 (PDT), Matthew Jacob > <mjacob@feral.com> said: > > >> On Sat, 26 Jun 1999 00:06:53 -0400, Douglas Gilbert > >> Given that we have clocked reasonably standard i386 hardware with fast > >> disks at 50 or 60 MB/sec through the filesystem, I doubt that the > >> indirect IO is the bottleneck in those cases. > > > Without cache pollution? > > Page cache pollution is a totally different issue. At 60MB/sec > we aren't even close to the performance levels where memory bandwidth > is an issue, so extra copies into the cache are irrelevant from a > bandwidth point of view. Of _course_ raw IO has less impact on > memory, but that's another point entirely.
What I mean was: raw I/O is an application policy statement that says "leaving this data in the buffer cache is not what I want". You certainly do have some overhead in throwing stuff away if it's sitting in the buffer cache.
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