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To: mingo@elte.hu
CC: jdike@addtoit.com, user-mode-linux-devel@lists.sourceforge.net,
       linux-kernel@vger.kernel.org
Subject: -rt doesn't compile for UML
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From: Miklos Szeredi <miklos@szeredi.hu>
Date: Wed, 28 Nov 2007 13:47:20 +0100
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When writing a big file to a ubd disk, everything in uml slows down to
a crawl, even though CPU usage is minimal.

So I wanted to try the latency tracer from -rt, but it doesn't compile
with UML:

  CC      arch/um/kernel/asm-offsets.s
In file included from arch/um/include/sysdep/kernel-offsets.h:2,
                 from arch/um/kernel/asm-offsets.c:1:
include/linux/sched.h: In function ‘set_tsk_need_resched_delayed’:
include/linux/sched.h:2105: error: ‘TIF_NEED_RESCHED_DELAYED’ undeclared (first use in this function)
include/linux/sched.h:2105: error: (Each undeclared identifier is reported only once
include/linux/sched.h:2105: error: for each function it appears in.)
include/linux/sched.h: In function ‘clear_tsk_need_resched_delayed’:
include/linux/sched.h:2110: error: ‘TIF_NEED_RESCHED_DELAYED’ undeclared (first use in this function)
include/linux/sched.h: In function ‘need_resched_delayed’:
include/linux/sched.h:2115: error: ‘TIF_NEED_RESCHED_DELAYED’ undeclared (first use in this function)
make[1]: *** [arch/um/kernel/asm-offsets.s] Error 1
make: *** [prepare0] Error 2

Ingo, do you think this route is worthwhile pursuing, or is it too
difficult to make -rt work for UML?

Thanks,
Miklos