Message-ID: <501F7904.4050206@linux.vnet.ibm.com>
Date: Mon, 06 Aug 2012 13:27:56 +0530
From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linuxppc-dev@ozlabs.org
Subject: Re: how to implement platform specific per process parameter?
References: <501F514C.2090909@ozlabs.ru>
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> There are 4 options:

> 1. [not a kernel interface] use ptrace to execute the register changing
> command inside the specified pid. The next context switch saves the new
> value in the thread_struct. Dirty hack.
> 
> 2. Add a new syscall which would receive pid + register value and do the
> job. A bit too much.
> 
> 3. Add some hook in /proc filesystem but so far there were no platform
> specific bits, right?
> 
> 4. Implement a static node "/sys/devices/system/cpu/dscr_control".
> write() would parse the input stream, call scanf("%d %x", &pid, &dscr)
> and do the job.
> 


/sys/ interface would be appropriate I believe. But in this way we can take a new
(pid, dscr) and update thread_struct. But there should be a way to enlist all
(pid, dscr) values which are explicitly set by the user and different than that
of /sys/devices/system/cpu/dscr_default. So that we can know which process is holding
to what value of DSCR at any point of time.

 
> What is the correct approach? Thanks.
> 
> 


Regards
Anshuman

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