Messages in this thread | | | Date | Thu, 10 Aug 2006 00:05:57 +0200 (CEST) | From | Esben Nielsen <> | Subject | Re: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8 |
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On Mon, 7 Aug 2006, Bill Huey wrote:
> On Mon, Aug 07, 2006 at 07:56:15PM -0700, Bill Huey wrote: >> On Thu, Aug 03, 2006 at 10:27:41AM -0400, Steven Rostedt wrote: >> >> ...(output and commentary a log deleted)... >> >>> This could also have a side effect that messes things up. >>> >>> Unfortunately, right now I'm assigned to other tasks and I cant spend >>> much more time on this at the moment. So hopefully, Ingo, Thomas or >>> Bill, or someone else can help you find the reason for this problem. >> >> Steve and company, >> >> Speaking of which, after talking to Steve about this and confirming this >> with a revert of changes. put_task_struct() can't deallocated memory from >> either the zone or SLAB cache without taking a sleeping lock. It can't >> be called directly from finish_task_switch to reap the thread because of >> that (violation in atomic). >> >> It is for this reason the RCU call back to delay processing was put into >> place to reap threads and was, seemingly by accident, missing from >> patch-2.6.17-rt7 to -rt8. That is what broke it in the first place. >> >> I tested it with a "make -j4" which triggers the warning and it they all >> go away now. >> >> Reverse patch attached: > > Resend with instrumentation code removed: > > bill > >
I had a long discussion with Paul McKenney about this. I opposed the patch from a latency point of view: Suddenly a high-priority RT task could be made into releasing a task_struct. It would be better for latencies to defer it to a low priority task.
The conclusion we ended up with was that it is not a job for the RCU system, but it ought to be deferred to some other low priority task to free the task_struct.
Esben
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