linux-kernel - Re: [PATCH/RFC] replace get_scheduled_cycles with sched_clock paravirt

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Date:	Fri, 16 Mar 2007 17:43:16 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Dan Hecht <dhecht@...are.com>, Zachary Amsden <zach@...are.com>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>
Subject: Re: [PATCH/RFC] replace get_scheduled_cycles with sched_clock paravirt_op

Andrew Morton wrote:
> On Wed, 14 Mar 2007 12:07:14 -0700 Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>   
>> Subject: Add a sched_clock paravirt_op
>>
>> The tsc-based get_scheduled_cycles interface is not a good match for
>> Xen's runstate accounting, which reports everything in nanoseconds.
>>
>> This patch replaces this interface with a sched_clock interface, which
>> matches both Xen and VMI's requirements.
>>
>> In order to do this, we:
>>    1. replace get_scheduled_cycles with sched_clock
>>    2. hoist cycles_2_ns into a common header
>>    3. update vmi accordingly
>>
>> One thing to note: because sched_clock is implemented as a weak function in
>> kernel/sched.c, we must define a real function in order to override this weak
>> binding.  This means the usual paravirt_ops technique of using an inline
>> function won't work in this case.
>>     
>
> include/asm/paravirt.h: In function 'paravirt_sched_clock':
> include/asm/paravirt.h:281: warning: implicit declaration of function 'PVOP_CALL0'
> include/asm/paravirt.h:281: error: expected expression before 'unsigned'
>   

Sorry, I didn't intend for it to be picked up; it depends on stuff
earlier in the patch series.  I just wanted to check with the VMI folks
that it works for them in principle.

    J

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