Re: [PATCH] 2.6.0 batch scheduling, HT aware

[Nick Piggin <piggin@cyberone.com.au>]

Con Kolivas wrote:

>I've done a resync and update of my batch scheduling that is also hyper-thread 
>aware.
>
>What is batch scheduling? Specifying a task as batch allows it to only use cpu 
>time if there is idle time available, rather than having a proportion of the 
>cpu time based on niceness.
>
>Why do I need hyper-thread aware batch scheduling?
>
>If you have a hyperthread (P4HT) processor and run it as two logical cpus you 
>can have a very low priority task running that can consume 50% of your 
>physical cpu's capacity no matter how high priority tasks you are running. 
>For example if you use the distributed computing client setiathome you will 
>be effectively be running at half your cpu's speed even if you run setiathome 
>at nice 20. Batch scheduling for normal cpus allows only idle time to be used 
>for batch tasks, and for HT cpus only allows idle time when both logical cpus 
>are idle.
>
>This is not being pushed for mainline kernel inclusion, but the issue of how 
>to prevent low priority tasks slowing down HT cpus needs to be considered for 
>the mainline HT scheduler if it ever gets included. This patch provides a 
>temporising measure for those with HT processors, and a demonstrative way to 
>handle them in mainline.
>

I wonder how does Intel suggest we handle this problem? Batch scheduling
aside, I wonder how to do any sort of priorities at all? I think POWER5
can do priorities in hardware, that is the only sane way I can think of
doing it.

I think this patch is much too ugly to get into such an elegant scheduler.
No fault to you Con because its an ugly problem.

How about this: if a task is "delta" priority points below a task running
on another sibling, move it to that sibling (so priorities via timeslice
start working). I call it active unbalancing! I might be able to make it
fit if there is interest. Other suggestions?