linux-kernel - Re: [PATCH] kthread: always create the kernel threads with normal priority

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Date:	Mon, 7 Jan 2008 16:53:18 +0100
From:	"Remy Bohmer" <linux@...mer.net>
To:	"Michal Schmidt" <mschmidt@...hat.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Jon Masters" <jcm@...hat.com>,
	"Satoru Takeuchi" <takeuchi_satoru@...fujitsu.com>,
	"Steven Rostedt" <rostedt@...dmis.org>
Subject: Re: [PATCH] kthread: always create the kernel threads with normal priority

Hello Michal,

> > Maybe we can find a way to use a similar mechanism as I used in my
> > patchset for the priorities of the remaining kthreads.
> > I do not like the way of forcing userland to change the priorities,
> > because that would require a userland with the chrt tool installed,
> > and that is not that practical for embedded systems (in which there
> > could be cases that there is no userland at all, or the init-process
> > is the whole embedded application). In that case an option to do it on
> > the kernel commandline is more practical.
> >
> > I propose this kernel cmd-line option:
> > kthread_pmap=somethread:50,otherthread:12,34
>
> I see. kthreadd would look up the priority for itself and
> kthread_create would consult the map for all other kernel threads.
> That should work.
> Your sirq_pmap would not be needed anymore, as kthread_pmap could be
> used for softirq threads too, right?

That is correct. The soft-irqs are just ordinary kernel-threads, but
irq_pmap is still needed, to set the priority of a certain interrupt
handler.
In this case it also possible to set the prio of the IRQ-kthreads as
well as the prio of a certain interrupt handler. This might give some
conflicts, and I have to check how to resolve these.

Kind Regards,

Remy


2008/1/7, Michal Schmidt <mschmidt@...hat.com>:
> On Mon, 7 Jan 2008 12:22:51 +0100
> "Remy Bohmer" <linux@...mer.net> wrote:
>
> > Hello Michal and Andrew,
> >
> > > Let's not make the decision for the user. Just allow the
> > > administrator to change kthreadd's priority safely if he chooses to
> > > do it. Ensure that the kernel threads are created with the usual
> > > nice level even if kthreadd's priority is changed from the default.
> >
> > Last year, I posted a patchset (that was meant for Preempt-RT at that
> > time) to be able to prioritise the interrupt-handler-threads (which
> > are kthreads) and softirq-threads from the kernel commandline. See
> > http://lkml.org/lkml/2007/12/19/208
> >
> > Maybe we can find a way to use a similar mechanism as I used in my
> > patchset for the priorities of the remaining kthreads.
> > I do not like the way of forcing userland to change the priorities,
> > because that would require a userland with the chrt tool installed,
> > and that is not that practical for embedded systems (in which there
> > could be cases that there is no userland at all, or the init-process
> > is the whole embedded application). In that case an option to do it on
> > the kernel commandline is more practical.
> >
> > I propose this kernel cmd-line option:
> > kthread_pmap=somethread:50,otherthread:12,34
>
> I see. kthreadd would look up the priority for itself and
> kthread_create would consult the map for all other kernel threads.
> That should work.
> Your sirq_pmap would not be needed anymore, as kthread_pmap could be
> used for softirq threads too, right?
>
> Michal
>
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