Precise: collapse gerneric and server into one flavour

[John Johansen]

On 10/14/2011 07:28 AM, Andy Whitcroft wrote:
> On Thu, Oct 13, 2011 at 11:13:47AM -0700, John Johansen wrote:
> 
>>> config PREEMPT_NONE
>>>         bool "No Forced Preemption (Server)"
>>>         help
>>>           This is the traditional Linux preemption model, geared towards
>>>           throughput. It will still provide good latencies most of the
>>>           time, but there are no guarantees and occasional longer delays
>>>           are possible.
>>>
>>>           Select this option if you are building a kernel for a server or
>>>           scientific/computation system, or if you want to maximize the
>>>           raw processing power of the kernel, irrespective of scheduling
>>>           latencies.
>>>
>>> config PREEMPT_VOLUNTARY
>>>         bool "Voluntary Kernel Preemption (Desktop)"
>>>         help
>>>           This option reduces the latency of the kernel by adding more
>>>           "explicit preemption points" to the kernel code. These new
>>>           preemption points have been selected to reduce the maximum
>>>           latency of rescheduling, providing faster application reactions,
>>>           at the cost of slightly lower throughput.
>>>
>>>           This allows reaction to interactive events by allowing a
>>>           low priority process to voluntarily preempt itself even if it
>>>           is in kernel mode executing a system call. This allows
>>>           applications to run more 'smoothly' even when the system is
>>>           under load.
>>>
>>>           Select this if you are building a kernel for a desktop system.
>>>
>> This isn't necessarily bad for a server either.  Its been a few years
>> since I really looked at the scheduler choices, so its worth looking into
>> again but voluntary preempt didn't have near as much overhead associated
>> with it as full preempt.
> 
> Perhaps we could do some comparative testing with these two, we did some
> timings before for HZ IIRC.  John was it you who did the HZ comparisons?
> 
yep, I think I still have the benchmarking set up, and could run it against
preempt, voluntary preempt, and generic