Messages in this thread Patch in this message | | | From | Con Kolivas <> | Subject | [PATCH] 2.6.1 Hyperthread smart "nice" 2 | Date | Mon, 2 Feb 2004 20:27:10 +1100 |
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Following on from the previous hyperthread smart nice patch;
>A while back we had an lkml thread about the problem of running low priority >tasks on hyperthread enabled cpus in SMP mode. Brief summary: If you run a >P4HT in uniprocessor mode and run a cpu intensive task at nice +20 (like >setiathome), the most cpu it will get during periods of heavy usage is about >8%. If you boot a P4HT in SMP mode and run a cpu intensive task at nice +20 >then if you run a task even at nice -20 concurrently, the nice +20 task will >get 50% of the cpu time even though you have a very high priority task. So >ironically booting in SMP mode makes your machine slower for running >background tasks.
Criticism was laid at the previous patch for the way a more "nice" task might never run on the sibling cpu if a high priority task was running. This patch is a much better solution.
What this one does is the following; If there is a "nice" difference between tasks running on logical cores of the same cpu, the more "nice" one will run a proportion of time equal to the timeslice it would have been given relative to the less "nice" task. ie a nice 19 task running on one core and the nice 0 task running on the other core will let the nice 0 task run continuously (102ms is normal timeslice) and the nice 19 task will only run for the last 10ms of time the nice 0 task is running. This makes for a much more balanced resource distribution, gives significant preference to the higher priority task, but allows them to benefit from running on both logical cores.
This seems to me a satisfactory solution to the hyperthread vs nice problem. Once again this is too arch. specific a change to sched.c for mainline, but as proof of concept I believe it works well for those who need something that works that they can use now.
http://ck.kolivas.org/patches/2.6/2.6.1/experimental/
The stuff on my website is incremental with my other experiments, but the attached patch applies cleanly to 2.6.1
Con --- linux-2.6.1-base/kernel/sched.c 2004-01-09 22:57:04.000000000 +1100 +++ linux-2.6.1-htn2/kernel/sched.c 2004-02-02 20:01:17.042394133 +1100 @@ -208,6 +208,7 @@ struct runqueue { atomic_t *node_nr_running; int prev_node_load[MAX_NUMNODES]; #endif + unsigned long cpu; task_t *migration_thread; struct list_head migration_queue; @@ -221,6 +222,10 @@ static DEFINE_PER_CPU(struct runqueue, r #define task_rq(p) cpu_rq(task_cpu(p)) #define cpu_curr(cpu) (cpu_rq(cpu)->curr) +#define ht_active (cpu_has_ht && smp_num_siblings > 1) +#define ht_siblings(cpu1, cpu2) (ht_active && \ + cpu_sibling_map[(cpu1)] == (cpu2)) + /* * Default context-switch locking: */ @@ -1380,6 +1385,10 @@ void scheduler_tick(int user_ticks, int cpustat->iowait += sys_ticks; else cpustat->idle += sys_ticks; + if (rq->nr_running) { + resched_task(p); + goto out; + } rebalance_tick(rq, 1); return; } @@ -1536,6 +1545,20 @@ need_resched: if (!rq->nr_running) { next = rq->idle; rq->expired_timestamp = 0; +#ifdef CONFIG_SMP + if (ht_active) { + /* + * If a HT sibling task is sleeping due to + * priority reasons wake it up now + */ + runqueue_t *htrq; + htrq = cpu_rq(cpu_sibling_map[(rq->cpu)]); + + if (htrq->curr == htrq->idle && + htrq->nr_running) + resched_task(htrq->idle); + } +#endif goto switch_tasks; } } @@ -1555,6 +1578,42 @@ need_resched: queue = array->queue + idx; next = list_entry(queue->next, task_t, run_list); +#ifdef CONFIG_SMP + if (ht_active) { + runqueue_t *htrq; + htrq = cpu_rq(cpu_sibling_map[(rq->cpu)]); + task_t *htcurr; + htcurr = htrq->curr; + + /* + * If a user task with lower static priority than the + * running task on the hyperthread sibling is trying + * to schedule, delay it till there is equal timeslice + * left of the hyperthread task to prevent a lower priority + * task from using an unfair proportion of the physical + * cpu's resources. + */ + if (next->mm && htcurr->mm && !rt_task(next) && + ((next->static_prio > + htcurr->static_prio && htcurr->time_slice > + task_timeslice(next)) || rt_task(htcurr))) { + next = rq->idle; + goto switch_tasks; + } + + /* + * Reschedule a lower priority task + * on the HT sibling, or wake it up if it has been + * put to sleep for priority reasons. + */ + if ((htcurr != htrq->idle && + htcurr->static_prio > next->static_prio) || + (rt_task(next) && !rt_task(htcurr)) || + (htcurr == htrq->idle && htrq->nr_running)) + resched_task(htcurr); + } +#endif + if (next->activated > 0) { unsigned long long delta = now - next->timestamp; @@ -2809,6 +2868,7 @@ void __init sched_init(void) prio_array_t *array; rq = cpu_rq(i); + rq->cpu = (unsigned long)(i); rq->active = rq->arrays; rq->expired = rq->arrays + 1; spin_lock_init(&rq->lock); | |