From: Wolfgang Grandegger <wg@grandegger.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Luotao Fu <l.fu@pengutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
RT <linux-rt-users@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue?
Date: Sun, 06 Jul 2008 11:41:28 +0200 [thread overview]
Message-ID: <48709348.6000101@grandegger.com> (raw)
In-Reply-To: <Pine.LNX.4.58.0807052041350.8466@gandalf.stny.rr.com>
Steven Rostedt wrote:
> On Wed, 2 Jul 2008, Wolfgang Grandegger wrote:
>> I removed all "likely" and "unlikely" macros, but the latencies did not
>> improve. Then I added
>>
>> preempt_disable();
>> preempt_enable();
>>
>> at the two locations mentioned above, like trace_mark() does, and
>> disabled CONFIG_RCU_TRACE. That helped to keep the latencies low, and it
>> did for 2.6.25.8-rt7 as well. As I see it, adding preemption points seem
>> to prevent high latencies.
>
> This to me sounds like we have preempt_enable_noresched someplace that
> shouldn't. In otherwords, we enabled preemption without checking if
> preemption is needed, which is a serious bug in -rt.
Yep, in 2.6.25.8-rt7 trace_mark() is not used any more, maybe for that
reason. Nevertheless, this "bug" kept the latency on my MPC5200 box low.
I will try with the old tracer to understand what the real cause of the
high latencies is (with CONFIG_RCU_TRACE disabled).
Wolfgang.
next prev parent reply other threads:[~2008-07-06 9:40 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-17 4:27 2.6.24-rc8-rt1 Steven Rostedt
2008-01-17 5:26 ` 2.6.24-rc8-rt1 Mark Knecht
2008-01-17 10:13 ` 2.6.24-rc8-rt1 Wolfgang Grandegger
2008-01-17 12:46 ` 2.6.24-rc8-rt1 Luotao Fu
2008-01-17 16:17 ` 2.6.24-rc8-rt1 Daniel Walker
2008-01-17 18:17 ` 2.6.24-rc8-rt1 Wolfgang Grandegger
2008-01-17 18:30 ` 2.6.24-rc8-rt1 Daniel Walker
2008-01-17 18:44 ` 2.6.24-rc8-rt1 Steven Rostedt
2008-01-17 18:45 ` 2.6.24-rc8-rt1 Steven Rostedt
2008-01-17 20:01 ` 2.6.24-rc8-rt1 Wolfgang Grandegger
2008-01-17 18:46 ` 2.6.24-rc8-rt1 Wolfgang Grandegger
2008-01-17 21:11 ` 2.6.24-rc8-rt1 Robert Schwebel
2008-01-17 21:36 ` 2.6.24-rc8-rt1 Wolfgang Grandegger
2008-01-23 14:53 ` 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc Luotao Fu
2008-01-23 15:50 ` Daniel Walker
2008-01-23 16:36 ` Wolfgang Grandegger
2008-01-24 10:53 ` Wolfgang Grandegger
2008-01-28 15:11 ` Luotao Fu
2008-01-28 15:38 ` Wolfgang Grandegger
2008-01-29 12:13 ` 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue? Luotao Fu
2008-01-29 13:38 ` Wolfgang Grandegger
2008-01-30 1:07 ` Paul E. McKenney
2008-01-30 8:18 ` Wolfgang Grandegger
2008-01-30 10:22 ` Paul E. McKenney
2008-01-30 10:45 ` Wolfgang Grandegger
2008-01-30 10:57 ` Paul E. McKenney
2008-01-30 11:15 ` Luotao Fu
2008-07-01 14:27 ` Wolfgang Grandegger
2008-07-01 15:11 ` Steven Rostedt
2008-07-01 16:11 ` Wolfgang Grandegger
2008-07-01 21:11 ` Luotao Fu
2008-07-02 11:03 ` Wolfgang Grandegger
2008-07-06 0:42 ` Steven Rostedt
2008-07-06 9:41 ` Wolfgang Grandegger [this message]
2008-07-08 15:08 ` Luotao Fu
2008-07-08 19:43 ` Wolfgang Grandegger
2008-07-09 12:53 ` Luotao Fu
2008-07-09 13:15 ` Wolfgang Grandegger
2008-07-09 14:52 ` Luotao Fu
2008-07-10 7:50 ` Wolfgang Grandegger
2008-08-01 21:09 ` Paul E. McKenney
2008-08-01 21:09 ` Paul E. McKenney
2008-08-05 15:40 ` Wolfgang Grandegger
2008-07-02 8:09 ` Wolfgang Grandegger
2008-07-06 0:39 ` Steven Rostedt
2008-07-06 9:34 ` Wolfgang Grandegger
2008-01-30 11:22 ` Wolfgang Grandegger
2008-01-17 19:57 ` 2.6.24-rc8-rt1 Mariusz Kozlowski
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