82xx performance

[Milton Miller]

On Jul 25, 2008, at 3:41 PM, Rune Torgersen wrote:

>> From: Arnd Bergmann [mailto:arnd at arndb.de]
>> On Thursday 17 July 2008, Rune Torgersen wrote:
>>> Arnd Bergmann wrote:
>>>> So again, nothing conclusive. I'm running out of ideas.
>>>
>>> Is the syscall path different or the same on ppc and powerpc?
>>> Any differences in the task switching, irq handling or page fault
>>> handling?
>>>
>>
>> It's all different in suble ways, but those changes should only
>> show up in the system time accounting, not user time accounting.
>
> I've been running the workload this board will see. On a 2.6.18 kernel
> %idle is ~50% and %wa (waiting for IO) is less than 1% most of the 
> time.
> On 2.6.25, the idle% is lower (by about 10-15%) and the %wa is
> consistently hovering around 20-30% sometimes spiking to 100%.
>
> The workload involves quite a bit of socket IO (TCP, UDP, Unix Sockets
> and TIPC) and disk IO.
> Any easy way of finding what is causing the wait for IO?
>
> (Ive been trying to get lttng to work, but not any good results so 
> far).

In both idle and wait, the cpu is in the idle loop waiting for something
to do.  The difference is that a cpu is considered in disk wait if the
there is a task in uninterruptible sleep that is not being counted as
waiting on another cpu.

With a significant change in wait time, I would suggest restating the
current observations to the linux-mm community, probably with a cc
to linux-kernel.

Be sure to state what you have done to equalize the comparison (eg
highmen, ram size left, etc).

There may be some tunables that could adjust the behavior.

milton