Red Hat Bugzilla – Bug 64525
Lack of dma on cdrom drives causes extremely poor interactive performance
Last modified: 2014-03-16 22:27:24 EDT
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.0+) Gecko/20020501 Description of problem: I fresh installed Redhat 7.3 today. I found while burning extra copies of Redhat 7.3 that with the new default of disabling dma on my cdrom drives caused extremely poor interactive performance. I have seen it seem to freeze and then job from 82% to 100% burning, and the mouse wouldn't move. By using hdparm -d1 /dev/hdc to reenable dma I was able to fix the problem. The comments in rc.sysinit suggest that dma on is problematic for some, but it is also problematic for others off. I also have read another bug report about skipjack beta that someone couldn't use their cd burner drive at all with dma disabled. I think the lines to disable dma on cdrom drives should be removed or at least commented out in a future release. Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: 1. login as a user 2. run xcdroast 3. select iso to burn 4. start burning iso Actual Results: The screen redraws slowly or freezes for seconds at a time. Expected Results: Interactively of X to be normal Additional info: I am noticed this while burning at 24X. I suspect that 4x wouldn't be that noticable, but 24X definitely is for me. I have a ABIT KT7A-RAID and the CDRW drive is on the secondary VIA IDE controller. I am using the default, out of the box/compiled by redhat, kernel for Redhat 7.3.
This was done intentionally, as many CD-ROM drives do not have proper DMA support. You can create /etc/sysconfig/harddisk<device> that has: USE_DMA=1 to reenable it on boot.