svn commit: r191643 - in head/sys: kern sys

[Jeff Roberson]

On Wed, 29 Apr 2009, Kostik Belousov wrote:

> On Wed, Apr 29, 2009 at 03:15:44AM +0000, Jeff Roberson wrote:
>> Author: jeff
>> Date: Wed Apr 29 03:15:43 2009
>> New Revision: 191643
>> URL: http://svn.freebsd.org/changeset/base/191643
>>
>> Log:
>>    - Remove the bogus idle thread state code.  This may have a race in it
>>      and it only optimized out an ipi or mwait in very few cases.
>>    - Skip the adaptive idle code when running on SMT or HTT cores.  This
>>      just wastes cpu time that could be used on a busy thread on the same
>>      core.
>>    - Rename CG_FLAG_THREAD to CG_FLAG_SMT to be more descriptive.  Re-use
>>      CG_FLAG_THREAD to mean SMT or HTT.
>>
>>   Sponsored by:   Nokia
>>
>> Modified:
>>   head/sys/kern/sched_ule.c
>>   head/sys/kern/subr_smp.c
>>   head/sys/sys/smp.h
>
> Now I see a reason why it is better #ifdef SMP the code that uses CG_FLAG_*.
> Also, we should check for tdq_cg != NULL in one more place.
>
> See the patch below, instead of exposing CG_FLAG_* for !SMP configs.

Thank you kan.  I did something slightly different so we can retain the 
adaptive idling on UP.

Thanks,
Jeff

>
> diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
> index 680572d..fe3a119 100644
> --- a/sys/kern/sched_ule.c
> +++ b/sys/kern/sched_ule.c
> @@ -891,6 +891,7 @@ tdq_move(struct tdq *from, struct tdq *to)
> 	return (1);
> }
>
> +#ifdef SMP
> /*
>  * This tdq has idled.  Try to steal a thread from another cpu and switch
>  * to it.
> @@ -947,6 +948,7 @@ tdq_idled(struct tdq *tdq)
> 	spinlock_exit();
> 	return (1);
> }
> +#endif
>
> /*
>  * Notify a remote cpu of new work.  Sends an IPI if criteria are met.
> @@ -2525,7 +2527,9 @@ sched_idletd(void *dummy)
> 	struct thread *td;
> 	struct tdq *tdq;
> 	int switchcnt;
> +#ifdef SMP
> 	int i;
> +#endif
>
> 	mtx_assert(&Giant, MA_NOTOWNED);
> 	td = curthread;
> @@ -2543,7 +2547,9 @@ sched_idletd(void *dummy)
> 		 * loops while on SMT machines as this simply steals
> 		 * cycles from cores doing useful work.
> 		 */
> -		if ((tdq->tdq_cg->cg_flags & CG_FLAG_THREAD) == 0 &&
> +#ifdef SMP
> +		if (tdq->tdq_cg != NULL &&
> +		    (tdq->tdq_cg->cg_flags & CG_FLAG_THREAD) == 0 &&
> 		    switchcnt > sched_idlespinthresh) {
> 			for (i = 0; i < sched_idlespins; i++) {
> 				if (tdq->tdq_load)
> @@ -2551,6 +2557,7 @@ sched_idletd(void *dummy)
> 				cpu_spinwait();
> 			}
> 		}
> +#endif
> 		switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
> 		if (tdq->tdq_load == 0)
> 			cpu_idle(switchcnt > 1);
>