From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Date: Thu, 11 Jul 2002 09:31:28 +0000 Subject: [Linux-ia64] Re: O(1) scheduler "complex" macros Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Wed, 10 Jul 2002, Erich Focht wrote: > > the best solution might be to just lock the 'next' task - this needs a new > > per-task irq-safe spinlock, to avoid deadlocks. This way whenever a task > > is in the middle of a context-switch it cannot be scheduled on another > > CPU. > > We tested this and it looked good. But inserting a udelay(100) like: > ... > prepare_arch_switch(rq, next); > udelay(100); > prev = context_switch(prev, next); > ... > leads to a crash after 10 minutes. Again this looks like accessing an > empty page. there is one more detail - wait_task_inactive() needs to consider the ->switch_lock as well - otherwise exit() might end up freeing the pagetables earlier than the context-switch has truly finished. The udelay(100) test should trigger this race. i've fixed this and uploaded the -A8 patch: http://redhat.com/~mingo/O(1)-scheduler/sched-2.5.25-A8 does this fix the ia64 crashes? you need to define an ia64-specific task_running(rq, p) macro, which should be something like: #define task_running(rq, p) \ ((rq)->curr = (p)) && !spin_is_locked(&(p)->switch_lock) a number of other places needed to be updated to use the task_running() macro. For load_balance() and set_cpus_allowed() it's technically not necessery, but i've added it to make things cleaner and safer for the time being. the default locking is still as lightweight as it used to be. > Does anything speak against such a test? It is there just to show up > quickly problems which we might normally get only after hours of > running. the udelay() test should be fine otherwise. (as long as ia64 udelay doesnt do anything weird.) Ingo