[Bug 381300] Re: elevator=cfq (default) cause starvation with very slow devices

Andrea Bravetti andreabravetti at gmail.com
Thu May 28 19:09:52 UTC 2009


** Description changed:

  Binary package hint: linux-image
  
  I had many performance problems using a usb pendrive:
  writing large files cause a system slowdown sometimes unacceptable.
  
  I performed several tests and in the end the culprit was found to
  be the CFQ scheduler which is used by default since 2.6.18...
  
  CFQ may be good on large system (but I'm not sure), but on a desktop
  with one (or two) cpu and only one disk it is unacceptable.
  
  If you are unsure try something like "dd if=/dev/zero of=/dev/sdx" where
  /dev/sdx is a 4gb pendrive, then try opening a web page... panic!
  
  No, not "kernel panic" but "user panic" is guaranteed!
  
  Any user that will try ubuntu and need to use a pendrive will
  think that it work like a floppy disk on win95...
  
  For a long time I believed it was a driver problem, but now
  I'm sure it depends on the scheduler, in fact, I resolved it just
  adding "elevator=noop".
  
- Please, consider the possibility of moving to elevator=noop or
- elevator=as, (if you care the desktop experience) at least for
- the "desktop" version if not for the "server"...
+ If you care the desktop experience, please, consider the possibility
+ of moving to elevator=noop or elevator=as, at least for the "desktop"
+ version if not for the "server"...
  
  I'm having this problem with any ubuntu version with kernel >= 2.6.18
  and actually I'm on jaunty with karmic's 2.6.30...
  
  A nice lecture:
  http://www.redhat.com/magazine/008jun05/features/schedulers/

-- 
elevator=cfq (default) cause starvation with very slow devices
https://bugs.launchpad.net/bugs/381300
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