Date: Sat, 06 Nov 1999 05:10:56 -0600 From: Rob Snow <rsnow@lgc.com> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu> Cc: freebsd-questions@freebsd.org Subject: Re: writing much slower than reading... Message-ID: <38240CC0.8099D19D@lgc.com> References: <19991106013045.13836@hydrogen.fircrest.net>
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Emm, I want your system. Have you double checked your numbers? They
look a bit high. Here's what I get on a vinum stripe across two 'cudas
on an SMP box:
rsnow@basil% time dd if=/dev/vinum/rstripe of=/dev/null bs=64k
count=2048
2048+0 records in
2048+0 records out
134217728 bytes transferred in 7.938773 secs (16906609 bytes/sec)
0.007u 0.520s 0:07.98 6.5% 73+371k 2+0io 0pf+0w
-Rob
John-Mark Gurney wrote:
>
> 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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