linux-kernel - Re: "RT_PREEMPT for loongson" is updated to patch-2.6.29.1-rt8

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Message-Id: <1240237323.8884.42.camel@falcon>
Date:	Mon, 20 Apr 2009 22:22:03 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	Zhang Le <r0bertz@...too.org>, linux-kernel@...r.kernel.org,
	Nicholas Mc Guire <hofrat@...r.at>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, zhangfx@...ote.com,
	loongson-dev@...glegroups.com, yanh@...ote.com,
	linux-mips@...ux-mips.org, linux-rt-users@...r.kernel.org
Subject: Re: "RT_PREEMPT for loongson" is updated to patch-2.6.29.1-rt8

On Mon, 2009-04-20 at 15:10 +0200, Ralf Baechle wrote:
> On Mon, Apr 20, 2009 at 10:01:55AM +0200, Ralf Baechle wrote:
> 
> > > I have divided ftrace to several commits in the above git tree, hope you
> > > can check it, thx :-) 
> > > 
> > > in addition to the static/dynamic/graph function tracer & system call
> > > tracer implementation, a mips specific ring_buffer_time_stamp
> > > (kernel/trace/ring_buffer.c) is also implemented to get 1us precision
> > > time, this is very important to make ftrace available in mips,
> > > otherwise, we can only get 1ms precision time for the original
> > > ring_buffer_time_stamp is based on sched_clock(jiffies based). 
> > > 
> > > perhaps we can implement a more precise sched_clock directly, just as
> > > x86 does(native_sched_clock, tsc based), but in mips, there is only a
> > > 32bit timer count which will quickly overflow, so it will need an extra
> > > overflow protection, which may influence the other parts of the kernel.
> > 
> > My git clone is still running to I'm commenting only on the patches you
> > posted earlier.  #ifdef-MIPS'ing things into the generic kernel code
> > definately won't be an acceptable way to get µs resolution.
> 

just fix it via moving mips specific ring_buffer_time_stamp to
arch/mips/kernel/ftrace.c via defining the original one as
__attribute__(weak).

in arch/mips/kernel/ftrace.c: 

u64 native_ring_buffer_time_stamp(...) {
...
}
u64 ring_buffer_time_stamp(...)
__attribute__((alias("native_ring_buffer_time_stamp")));

in kernel/trace/ring_buffer.c:

-u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+ u64 __attribute__((weak)) ring_buffer_time_stamp(struct ring_buffer
*buffer, int cpu)

*** not push to the git tree yet.

> In changeset e67f78d663a84ef93aa12c3c8c1adf3033c4f9a1 you introduce
> <asm/rwsem.h> but because RWSEM_GENERIC_SPINLOCK is always set that file
> won't ever be included.
> 

Yes, currently, I'm trying to fix it.

>   Ralf

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