From: Srivatsa Vaddagiri <vatsa@in.ibm.com>
To: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Zwane Mwaikambo <zwane@arm.linux.org.uk>,
Nathan Lynch <nathanl@austin.ibm.com>,
Joel Schopp <jschopp@austin.ibm.com>,
Ashok Raj <ashok.raj@intel.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Gautham R Shenoy <ego@in.ibm.com>, Ingo Molnar <mingo@elte.hu>,
paulmck@us.ibm.com
Subject: Re: [BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes
Date: Tue, 8 May 2007 09:40:33 +0530 [thread overview]
Message-ID: <20070508041033.GB25030@in.ibm.com> (raw)
In-Reply-To: <874pmoro1c.wl%takeuchi_satoru@jp.fujitsu.com>
On Tue, May 08, 2007 at 12:29:19PM +0900, Satoru Takeuchi wrote:
> > We used to be able to create kernel threads higher than any userspace
> > priority. If this is no longer true, I think that's OK: equal priority
> > still means we'll get scheduled, right?
>
> IF SCHED_RR, yes. However, if SCHED_FIFO, no. Such process doen't have timeslice
> and only relinquish CPU time voluntarily.
yeah ..this is truly a problem if SCHED_FIFO user-space cpu hog task is
running at MAX_USER_RT_PRIO (which happens to be same as max real-time
priority kernel threads can attain - MAX_RT_PRIO).
One option is to make MAX_USER_RT_PRIO < MAX_RT_PRIO. I am not sure what
semantics that will break (perhaps the real-time folks can clarify
that).
The other easier option is to add a wake_up_process_to_front() API in
sched.c, which essentially wakes up the process and enqueues the task to
the front of runqueue.
> # Hence this problem is complicated ;-(
--
Regards,
vatsa
next prev parent reply other threads:[~2007-05-08 4:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-07 10:10 [BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes Satoru Takeuchi
2007-05-07 10:47 ` Gautham R Shenoy
2007-05-07 11:02 ` Srivatsa Vaddagiri
2007-05-07 12:39 ` Gautham R Shenoy
2007-05-07 10:55 ` Srivatsa Vaddagiri
2007-05-07 10:56 ` KAMEZAWA Hiroyuki
2007-05-07 13:42 ` Rusty Russell
2007-05-08 2:41 ` Satoru Takeuchi
2007-05-08 3:02 ` Rusty Russell
2007-05-08 3:29 ` Satoru Takeuchi
2007-05-08 4:04 ` Rusty Russell
2007-05-08 4:10 ` Srivatsa Vaddagiri [this message]
2007-05-08 7:16 ` Satoru Takeuchi
2007-05-08 16:48 ` Srivatsa Vaddagiri
2007-05-09 0:40 ` Satoru Takeuchi
2007-05-09 0:47 ` Nick Piggin
2007-05-09 6:31 ` Satoru Takeuchi
2007-05-09 8:56 ` Gautham R Shenoy
2007-05-11 8:49 ` [PATCH 1/2] Fix stop_machine_run problem with naughty real time process Satoru Takeuchi
2007-05-11 9:18 ` Satoru Takeuchi
2007-05-11 8:49 ` [PATCH 2/2] cpu hotplug: fix ksoftirqd termination on cpu hotplug with naughty realtime process Satoru Takeuchi
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