Messages in this thread | | | Subject | Re: Indirect IO in Linux, some figures | Date | Mon, 05 Apr 1999 10:52:18 -0700 | From | "Gregory P. Smith" <> |
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> The computer was an AMD K6-2 300MHz, super 7 motherboard (Via) with > 64MB of PCI-100 RAM. An Advansys 940UW SCSI adapter was used with an > IBM DCHS04U ultra wide disk. ...... > So I guess the assertion that you need direct IO for 100MB/sec > throughput is supported by these figures.
That makes sense. Look at the I/O bandwidth of your CPU. To do the copy_to/from_user it takes coping the data -in- to the CPU as well as copying it back -out- of the CPU. This is time and bus bandwidth consuming. Even if you have a recent system (P2 or P3 with 100Mhz bus, possibly even a K6-2 or K6-3 with a 100Mhz bus) this takes a lot of the bus bandwidth that would presumably be better off used for the processing of the data rather than the simple copying of it. You can only send or receive data at that rate for a short time before your low on memory and need to do something with it...
Intel x86 CPUs still fall pretty far behind in the I/O bandwidth per CPU category. This is where the newest Alpha's and other higher end systems shine.
Greg
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