Cyril Plisko wrote:
> On Thu, Oct 30, 2008 at 7:15 PM, Sumit Gupta <[EMAIL PROTECTED]> wrote:
>
>> On Oct 30, 2008, at 9:25 AM, Cyril Plisko wrote:
>>
>>
>>> On Thu, Oct 30, 2008 at 6:01 PM, Sumit Gupta <[EMAIL PROTECTED]> wrote:
>>>
>>>> Hi Cyril
>>>>
>>>> The LU entry points are called using kernel threads (called worker
>>>> threads
>>>> inside the framework). The thread pool is dynamically grown from 4 to 256
>>>> (a
>>>> soft limit) by stmf based on the load. The task spread is round robin
>>>> among
>>>> all the workers. Regarding sleeping, the framework is designed to allow
>>>> for
>>>> both synchronous and asynchronous operations. You can choose a model
>>>> which
>>>> is best for your application. As a guideline, if you have to sleep for
>>>> several milliseconds, you should not block the worker thread and use the
>>>> lu_poll entry point (by calling stmf_task_poll_lu()). But if your sleep
>>>> is
>>>> just to implement synchronous operations and your backend is reasonably
>>>> fast, its ok to block the worker.
>>>>
>>> Sumit,
>>>
>>> thanks for explanation. As for the duration of the sleep - I was
>>> wondering about calling kmem_alloc() with KM_SLEEP vs KM_NOSLEEP
>>> inside LU entry point. I have no idea how long this will sleep.
>>>
>> It is ok to use KM_SLEEP inside LU entry points as in most cases you
>> will have memory and the call wont sleep. If you are running out of memory
>> then your system performance is not going to be good anyway. Which is what
>> will happen if the worker sleeps for a long time.
>>
>>
>
> I see, thanks.
>
One more thing I forgot to mention is that you should use
lu_task_alloc entry point to do most of your per-task allocations. The
benefit is that those allocations are cached by the framework and you
wont do them again and again for the subsequent tasks. The cache is
automatically drained (slowly) by stmf (by calling lu_task_free entry
point) after few seconds of inactivity.
>
>
>>> I also didn't quite grok your note on using lu_poll. Can you please
>>> give some example ?
>>>
>> The framework provides a mechanism for the LU to say "I cannot handle
>> this task right now, call me back later". The LU does so by calling
>> stmf_task_poll_lu() and the framework later on calls the lu_poll entry
>> point. This is useful for very slow tasks like rewinding a tape or ejecting
>> media etc. This is also documented in detail in the stmf spec.
>>
>
> I think I need to spend some more time with the spec. BTW, v1.4 that
> is published on os.org - is it the latest spec ?
>
Yup. Thats the latest.
Sumit
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