[dm-devel] [PATCH 1/2] dm-kcopyd: introduce per-module throttle structure
Joe Thornber
thornber at redhat.com
Mon Jun 13 09:17:16 UTC 2011
On Sat, Jun 11, 2011 at 04:27:02PM -0400, Mikulas Patocka wrote:
> It is much easier to explain to the users "if you set X value in
> /sys/module/dm_mirror/parameters/raid1_resync_throttle, then the copying
> will be done in X% of time, leaving the disk idle 100-X% of time", then to
> invent some magic mechanisms that change multiple things based on X and
> other conditions.
Yes, that is very easy to explain to the users. This sort of
description is what I was after when I kept asking you to tell me how
to set it.
It's not clear to me that setting the throttle to 80% will copy at 80%
of the speed, or leave the disk idle for 20% of the time. Perhaps you
have some benchmarks to back this up? (with different memory pressure
situations please).
Restricting the cpu available to issue io is not a great way to
throttle io. There will be plenty of situations where 20% of the cpu
is enough to swamp the devices.
- Joe
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