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From: Ingo Molnar <mingo@elte.hu>
To: Mark_H_Johnson@raytheon.com
Cc: Karsten Wiese <annabellesgarden@yahoo.de>,
	Bill Huey <bhuey@lnxw.com>, Adam Heath <doogie@debian.org>,
	"K.R. Foley" <kr@cybsft.com>,
	linux-kernel@vger.kernel.org,
	Florian Schmidt <mista.tapas@gmx.net>,
	Fernando Pablo Lopez-Lezcano <nando@ccrma.Stanford.EDU>,
	Lee Revell <rlrevell@joe-job.com>,
	Rui Nuno Capela <rncbc@rncbc.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Michal Schmidt <xschmi00@stud.feec.vutbr.cz>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1
Date: Thu, 4 Nov 2004 16:19:48 +0100	[thread overview]
Message-ID: <20041104151948.GA25326@elte.hu> (raw)
In-Reply-To: <20041104151631.GA24056@elte.hu>


* Ingo Molnar <mingo@elte.hu> wrote:

> icmp/ping replies are handled by ksoftirqd. Once a networking request
> has been handed to ksoftirqd it cannot be redirected to another CPU,
> because softirq processing is fundamentally per-CPU. So if the network
> interrupt hits the CPU where the RT-task is running then the RT task
> will starve that ksoftirq instance (and hence the reply) even if
> another CPU in the system is idle.
> 
> i agree that this is an SMP/RT artifact that should be fixed. hardirq
> workload can be redirected to other CPUs because it's single-threaded,
> but it's not that easy for softirq workload.
> 
> i suspect the same phenomenon causes some of the other scheduling
> artifacts ('frozen' X) you've noticed.

does the ping phenomenon go away if you chrt both the networking IRQ
thread and both ksoftirqd's to above the RT task's priority? (this
doesnt solve the problem though - that task has RT priority for a reason
and on an SMP box the kernel should be able to schedule work without
getting into this starvation scenario.)

	Ingo

  reply	other threads:[~2004-11-04 15:21 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-11-04 15:02 [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1 Mark_H_Johnson
2004-11-04 15:16 ` Ingo Molnar
2004-11-04 15:19   ` Ingo Molnar [this message]
  -- strict thread matches above, loose matches on Subject: below --
2004-11-04 19:39 Mark_H_Johnson
2004-11-04 19:52 ` Ingo Molnar
2004-11-04 17:52 Mark_H_Johnson
2004-11-04 16:53 Mark_H_Johnson
2004-11-04 16:22 Mark_H_Johnson
2004-11-04 16:30 ` Ingo Molnar
2004-11-04 16:32   ` Ingo Molnar
2004-11-04 18:59     ` john cooper
2004-11-04 19:44       ` Ingo Molnar
2004-11-04 23:25         ` john cooper
2004-11-05 21:42         ` Scott Wood
2004-11-05 22:36           ` Bill Huey
2004-11-08 14:35             ` Esben Nielsen
2004-11-08 15:42               ` Ingo Molnar
2004-11-08 22:47               ` Bill Huey
2004-11-06  7:42           ` Ingo Molnar
2004-11-04 16:04 Mark_H_Johnson
2004-11-04 16:13 ` Ingo Molnar
2004-11-04 16:17 ` Ingo Molnar
2004-11-03 20:40 Mark_H_Johnson
2004-11-03 18:24 Mark_H_Johnson
2004-10-18 14:50 [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5 Ingo Molnar
2004-10-19 12:46 ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U6 Ingo Molnar
2004-10-19 18:00   ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U7 Ingo Molnar
2004-10-20  9:45     ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8 Ingo Molnar
2004-10-21 13:27       ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9 Ingo Molnar
2004-10-22 13:35         ` [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9.3 Ingo Molnar
2004-10-22 15:50           ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-U10 Ingo Molnar
2004-10-22 17:56             ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-U10.2 Ingo Molnar
2004-10-25 10:40               ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0 Ingo Molnar
2004-10-27  0:15                 ` [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.3 Ingo Molnar
2004-11-03 10:58                   ` [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1 Ingo Molnar
2004-11-03 13:44                     ` Lorenzo Allegrucci
2004-11-03 13:46                       ` Ingo Molnar
2004-11-03 17:53                         ` Lorenzo Allegrucci
2004-11-03 20:41                           ` Lorenzo Allegrucci
2004-11-03 20:43                             ` Ingo Molnar
2004-11-03 21:05                               ` Lorenzo Allegrucci
2004-11-03 19:33                     ` john cooper
2004-11-03 23:03                     ` Magnus Naeslund(t)
2004-11-04  6:56                       ` Ingo Molnar
2004-11-04 19:34                     ` Gunther Persoons
2004-11-04 20:31                       ` Chris Friesen

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