time slice cfq comments

From: Con Kolivas
Date: Fri Dec 10 2004 - 17:27:34 EST


Hi Jens

Just thought I'd make a few comments about some of the code in your time sliced cfq.

+ if (p->array)
+ return min(cpu_curr(task_cpu(p))->time_slice,
+ (unsigned int)MAX_SLEEP_AVG);

MAX_SLEEP_AVG is basically 10 * the average time_slice so this will always return task_cpu(p)->time_slice as the min value (except for the race you described in your comments). What you probably want is

+ return min(cpu_curr(task_cpu(p))->time_slice,
+ (unsigned int)DEF_TIMESLICE);


Further down you do:
+ /*
+ * for blocked tasks, return half of the average sleep time.
+ * (because this is the average sleep-time we'll see if we
+ * sample the period randomly.)
+ */
+ return NS_TO_JIFFIES(p->sleep_avg) / 2;

unfortunately p->sleep_avg is a non-linear value (weighted upwards towards MAX_SLEEP_AVG). I suspect here you want

+ return NS_TO_JIFFIES(p->sleep_avg) / MAX_BONUS;

I don't see any need for / 2.

Cheers,
Con
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