Date: Sun, 19 Sep 1999 11:37:23 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: dg@root.com, Greg Lehey <grog@lemis.com>, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: User block device access (was: cvs commit: src/sys/miscfs/specfs spec_vnops.c src/sys/sys vnode.h src/sys/kern vfs_subr.c) Message-ID: <199909191837.LAA73569@apollo.backplane.com> References: <17128.937765874@critter.freebsd.dk>
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:No that isn't the case, and if you cared to look at the code you
:would realize that the blocksize I use doesn't matter much since
:spec_read() reblocks.
:
:rover# time dd if=/dev/rda0 of=/dev/null bs=8k count=10000
:10000+0 records in
:10000+0 records out
:81920000 bytes transferred in 27.664275 secs (2961220 bytes/sec)
:0.0u 0.4s 0:27.66 1.4% 82+231k 0+0io 0pf+0w
:rover# ^rda^da^
:time dd if=/dev/da0 of=/dev/null bs=8k count=10000
:10000+0 records in
:10000+0 records out
:81920000 bytes transferred in 66.234151 secs (1236824 bytes/sec)
:0.0u 2.8s 1:06.24 4.2% 69+194k 40001+0io 0pf+0w
:
:> Also, if you
:> are only getting 3.1 MBytes/sec over the raw interface there's
:> something seriously screwy with your setup.
:
:Yes indeed there are: lack of funds for much needed HW upgrades.
:This is actually a 1.8G Quantum Prodrive I inherited when a former
:instance of freefall had a disk upgrade in early 1995 and currently
:the only scsi disk I have to test with.
:
:--
:Poul-Henning Kamp FreeBSD coreteam member
What kind of cpu is this? If the difference is this great, then
the memory-copy overhead is what is killing your test due to a slow
cpu. Since you are not using the buffered block device the way it
is supposed to be used (i.e. your test is resulting in a 100% cache
miss ratio), your results are a foregone conclusion. They aren't
really proving anything other then the fact that the buffered block
device is caching the data (incuring an extra copy) while the raw
device is not. This does not make the raw device somehow magically
better.
-Matt
Matthew Dillon
<dillon@backplane.com>
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