Messages in this thread Patch in this message | | | Date | Sat, 14 May 2005 11:30:12 -0500 | From | Nathan Lynch <> | Subject | Re: [Lse-tech] Re: [PATCH] cpusets+hotplug+preepmt broken |
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On Fri, May 13, 2005 at 07:58:51PM -0700, Paul Jackson wrote: > > So how would you, or Srivatsa or Nathan, respond to my more substantive > point, to repeat: > > Srivatsa, replying to Dinakar: > > This in fact was the reason that we added lock_cpu_hotplug > > in sched_setaffinity. > > Why just in sched_setaffinity()?
I suspect that the lock_cpu_hotplug is no longer necessary in sched_setaffinity. I found the original changeset which introduced it, and it's short enough that I'll just duplicate it here:
diff -Naru a/kernel/sched.c b/kernel/sched.c --- a/kernel/sched.c 2005-05-14 07:21:39 -07:00 +++ b/kernel/sched.c 2005-05-14 07:21:39 -07:00 @@ -1012,6 +1012,7 @@ unsigned long flags; cpumask_t old_mask, new_mask = cpumask_of_cpu(dest_cpu); + lock_cpu_hotplug(); rq = task_rq_lock(p, &flags); old_mask = p->cpus_allowed; if (!cpu_isset(dest_cpu, old_mask) || !cpu_online(dest_cpu)) @@ -1035,6 +1036,7 @@ } out: task_rq_unlock(rq, &flags); + unlock_cpu_hotplug(); } /* @@ -2309,11 +2311,13 @@ if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask))) return -EFAULT; + lock_cpu_hotplug(); read_lock(&tasklist_lock); p = find_process_by_pid(pid); if (!p) { read_unlock(&tasklist_lock); + unlock_cpu_hotplug(); return -ESRCH; } @@ -2334,6 +2338,7 @@ out_unlock: put_task_struct(p); + unlock_cpu_hotplug(); return retval; } # This is a BitKeeper generated diff -Nru style patch. # # ChangeSet # 2004/03/19 08:02:56-08:00 rusty@rustcorp.com.au # [PATCH] Hotplug CPUs: Take cpu Lock Around Migration # # Grab cpu lock around sched_migrate_task() and #sys_sched_setaffinity(). # This is a noop without CONFIG_HOTPLUG_CPU. # # The sched_migrate_task may have a performance penalty on NUMA if #lots # of exec rebalancing is happening, however this only applies to # CONFIG_NUMA and CONFIG_HOTPLUG_CPU, which noone does at the moment # anyway. # # Also, the scheduler in -mm solves the race another way, so this #will # vanish then. # # kernel/sched.c # 2004/03/16 18:10:10-08:00 rusty@rustcorp.com.au +5 -0 # Hotplug CPUs: Take cpu Lock Around Migration #
The lock/unlock_cpu_hotplug is no longer there in sched_migrate_task. The changelog leads me to believe that it was intended that the same change should have been made to sched_setaffinity by now. I think it's safe to remove it; I can't see why it would be necessary any more.
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