Hi Percentage of CPU usage in copying or writing large files

kaplan71 · 09-14-2006, 01:35 PM

Hi there --

I have Fedora Core 3 running on a Dell Dimension 9150 with 2 GB of RAM and I have noticed that whenever I copy or write a large file, the system slows down tremendously. Specifcally,
other applications and even moving the mouse take a much longer time to accomplish.

I ran the top command to see if I could localize the problem. I noticed that the wa field in top had percentages in the double digits when the copying or writing occurred while the swap field did not have any percentage of activity.

My first question is what is the wa field, and secondly what do I need to do to correct this problem? Thanks.

macemoneta · 09-14-2006, 01:54 PM

That's I/O wait. It usually means that DMA is disabled on the drive. You can check with (for example):

Code:

# hdparm -v /dev/hda

/dev/hda:
 multcount    = 16 (on)
 IO_support   =  1 (32-bit)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 readonly     =  0 (off)
 readahead    = 4096 (on)
 geometry     = 16383/255/63, sectors = 156301488, start = 0

To set DMA on:

hdparm -d1 /dev/hda

kaplan71 · 09-14-2006, 02:08 PM

Hi there --

Thanks for your reply. I tried running the hdparm command as root from runlevel 3, but I got
the error message: OPERATION NOT PERMITTED. Do I need to run in single-user mode to make the
change or is there something else to do? Thanks.

macemoneta · 09-14-2006, 02:14 PM

Do you have an IDE hard drive, or is it SCSI?

kaplan71 · 09-14-2006, 02:20 PM

The drive in question is IDE. I confirmed this in following manner:

I did a df command and the drive appeared as /dev/hda

I then ran fdisk and confirmed there as well the hardware path was /dev/hda.

kaplan71 · 09-14-2006, 02:24 PM

Hold everything --

I just found out from the user of the system, that the drives are SATA and not the standard PATA drives. If memory serves me correctly, there is a specific command or argument for these types of drives. Correct?

macemoneta · 09-14-2006, 02:33 PM

SATA drives generally don't need configuration (alway use DMA). However, check your BIOS - some configuration options (sometimes labeled "enhanced IDE" or similar) actually kill I/O performance on Linux. While you are at it, make sure you have the current Dell BIOS for that machine.

macemoneta · 09-14-2006, 02:39 PM

Another possible issue... The most recent FC3 kernel is 2.6.12 based. There were many SATA changes after that. You should consider upgrading to FC5 (use a re-spin to avoid having to download a ton of maintenance).

kaplan71 · 09-14-2006, 04:02 PM

Hi there --

I did do a check previous in the system BIOS and there was no reference to the Enhanced IDE performance. I'll double-check to make sure. The notion of upgrading the OS to Fedora Core 5
is probably the avenue that will be taken. Thanks for the information.