Re: Qustions about CPU usage of dd process
Pádraig Brady wrote: The CPU percentage of dd process sometimes is 30% to 50%, which is higher than we expect (= 20%), and there is no other big program running at the same time. If the disc in SATA ODD is CD-R instead of DVD-R, the percentage is much smaller(=20). That just means that dd is waiting on the CD-R more than on the DVD-R as the DVD-R is probably faster. iowait != busy. It's using cpu time to actively copy data around in ram or to/from IO ports if not using DMA, not waiting on the hardware. So my questions are: (1) Is there an official normal range(or criteria) to the dd CPU percentage? (2) Can we say that it's abnormal if it is higher than 30% or even 50%? (3) And what kinds of factors lead to the high CPU percentage of dd and how to decrease it? 1) No, it entirely depends on your hardware and kernel 2) I certainly don't like to see it even as high as 20% on typical desktop PC type hardware. I prefer to see it less than 5%. 3) Ideas include the small block size, hardware not using DMA, hardware generating a lot of interrupts/only transferring a single sector at a time. ___ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
Re: Qustions about CPU usage of dd process
On Dec 4, 2007 8:21 PM, Phillip Susi [EMAIL PROTECTED] wrote: Pádraig Brady wrote: The CPU percentage of dd process sometimes is 30% to 50%, which is higher than we expect (= 20%), and there is no other big program running at the same time. If the disc in SATA ODD is CD-R instead of DVD-R, the percentage is much smaller(=20). That just means that dd is waiting on the CD-R more than on the DVD-R as the DVD-R is probably faster. iowait != busy. It's using cpu time to actively copy data around in ram or to/from IO ports if not using DMA, not waiting on the hardware. I think you may have misunderstood Pádraig's point. Suppose that the kernel and dd between them need X units of CPU to process 1MB of data read from either type of disk.As the disk's data transfer rate rises, those X units of CPU will need to be used more often, because those 1MB chunks are arriving from the device at shorter intervals. For that reason, one would expect the CPU usage resulting from the use of a faster device to be greater, even if the same total amount of CPU work is needed to transfer the data in both cases. However, I have no idea if the extent of this effect is sufficient to explain the differences that you are seeing. James. ___ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
Qustions about CPU usage of dd process
Greetings: This is Shane, I'm sorry to disturb you guys. I have some questions which are about CPU usage percentage of dd process. I'm appreciated if you can give me some help or suggestion. When we do some test on our motherboards, we find that in some cases, the CPU usage percentage of dd is a little high when we dump data from SATA ODD DVD disc to SATA HDD: # dd if=/dev/cdwriter of=/root/temp.iso The CPU percentage of dd process sometimes is 30% to 50%, which is higher than we expect (= 20%), and there is no other big program running at the same time. If the disc in SATA ODD is CD-R instead of DVD-R, the percentage is much smaller(=20). So my questions are: (1) Is there an official normal range(or criteria) to the dd CPU percentage? (2) Can we say that it's abnormal if it is higher than 30% or even 50%? (3) And what kinds of factors lead to the high CPU percentage of dd and how to decrease it? BTW, my HW/SW Env: AMD SB700 + RS690 SAMSUNG SATA ODD Seagate SATA HDD RedHat RHEL5/RHEL4.6 and openSUSE10.3 Linux Thanks Best Regards Shane ___ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
