Date: Sat, 6 Nov 1999 01:30:45 -0800 From: John-Mark Gurney <gurney_j@efn.org> To: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: writing much slower than reading... Message-ID: <19991106013045.13836@hydrogen.fircrest.net>
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well, I am working on writing a capture program to do 640x480x12bpp@30fps
to a raw disk, but writing to the raw device is SOOO slow... the reason
I say it's slow is the fact that it takes 8 times the system time writing
than reading...
a bit about the system... k6/2-250, 100mhz system bus, pc100 64meg dimm,
VIA MVP3 chipset (IDE DMA enabled), IBM-DPTA-372730 hard disk, Hauppauge
WinCast/TV Model 61351 B226, 3.3-RELEASE...
now the hard disk can push and pull around 20meg/sec w/o any problems..
but when I time the disk I get:
$ time dd if=/dev/rwd0s1g of=/dev/null bs=64k count=2048
2048+0 records in
2048+0 records out
134217728 bytes transferred in 5.747521 secs (23352281 bytes/sec)
5.75 real 0.01 user 0.21 sys
$ time dd if=/dev/zero of=/dev/rwd0s1g bs=64k count=2048
2048+0 records in
2048+0 records out
134217728 bytes transferred in 6.281820 secs (21366057 bytes/sec)
6.28 real 0.00 user 1.68 sys
now, why does it cost SOOO much more processing time to write than
read?? are there plans to fix this slow down? is it possible? can't
we just dma write out of userland since we are blocking on the write?
--
John-Mark Gurney Voice: +1 408 975 9651
Cu Networking
"The soul contains in itself the event that shall presently befall it.
The event is only the actualizing of its thought." -- Ralph Waldo Emerson
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