2005/6/14, Randall R Schulz <rschulz@sonic.net>:
Ciro,
On Monday 13 June 2005 19:57, Ciro Iriarte wrote:
I'm running SuSE 9.2 on a Proliant DL380, was working fine, only had problems copy and entire tree from one FS to another (it seems to hang). The backup to tape was during 3 hours. The changes made (/boot/grub/menu.lst):
* Deleted the "desktop" kernel parameter
I did this on my 9.1 system even though I am running a desktop system. In "desktop" mode the kernel's scheduling quantum is reduced by a factor of ten to create more responsiveness, but it increases scheduling overhead by the same factor. Given a fast enough CPU (3 GHz, in my case), this does not seem to impair perceived responsiveness.
I'm not sure why, but my 9.3 installation did not include the "desktop" parameter. Maybe I removed it while installing and forgot doing so. Maybe it's no long enabled by default.
* Changed the "elevator" kernel parameter from "as" to "cfq"
This relates to how disk accesses are scheduled (ordered) when there are multiple outstanding I/O requests pending in the kernel disk queues. "CFQ" stands for "completely fair queuing" and "as" stands for "anticipatory scheduling". As the name suggests, the "anticipatory" scheduling has a stronger heuristic aspect and thus has more potential to be thwarted by access patterns not characteristic of the patterns it anticipates. The AS scheduler has several tunable parameters specific to it, too, so it's conceivable that there are values for those parameters that could give you even better performance than simply choosing CFQ.
There's some explanatory text in "/usr/src/linux/Documentation/block/as-iosched.txt" and "/usr/src/linux/Documentation/kernel-parameters.txt" that you might be able to use to conduct some more directed, informed experiments.
Now, the backups takes 1h 40 min to finish, any comments?
There's no arguing with success, I'd say. At least in this case. I'd also venture to guess that these kernel parameters will _not_ lead to optimal performance during normal interactive or server loads and that you'll want to use them only for your backup purposes
Ciro
Randall Schulz
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I noticed that SLES 9 comes with CFQ as the default scheduler CI.-