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Date: Thu, 28 Jun 2007 08:37:23 -0400 (EDT)
From: Steven Rostedt <rostedt@goodmis.org>
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To: Dan Williams <dan.j.williams@intel.com>
cc: Ingo Molnar <mingo@elte.hu>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
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       Dipankar Sarma <dipankar@in.ibm.com>,
       "David S. Miller" <davem@davemloft.net>, kuznet@ms2.inr.ac.ru
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues
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Hi Dan,

On Mon, 25 Jun 2007, Dan Williams wrote:

> Yes you are right, ARM does not flush L1 when prev==next in switch_mm.
>
> > Perhaps something else is at fault here.
> >
> I'll try and dig a bit deeper...

BTW:

 static int __init iop_adma_init (void)
 {
+       iop_adma_workqueue = create_workqueue("iop-adma");
+       if (!iop_adma_workqueue)
+               return -ENODEV;
+

Could you also try upping the prio of all the "iop-adma" threads?

You should see thread names such as (on SMP) "iop-adma/0", "iop-adma/1"
... "iop-adma/N" where N = # of CPUs - 1.

do a "chrt -p -f 98 <pid>"  once for each of the thread's PIDs.  The
chrt can be found in the package "util-linux" on Red Hat / Fedora, and in
schedutils on Debian.

It just dawned on me that workqueues don't run at a high priority by
default.  So it's funny that I'm running all my current tasklets as a low
priority work queues :-)

But that can certainly be a cause of high latency.  I need to update my
patches to make the workqueue thread a higher priority. All benchmarks on
this patch have been using a low priority work queue.

I also don't see any nice API to have the priority set for a workqueue
thread from within the kernel. Looks like one needs to be added,
otherwise, I need to have the wrapper dig into the workqueue structs to
find the thread that handles the workqueue.

Thanks,

-- Steve
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