Ian Lepore wrote:
>On Fri, 2017-10-06 at 19:02 +0000, Rick Macklem wrote:
>> I have now dropped the client side of Flexible File Layout for pNFS into head
>> and I believe it is basically working.
>> Currently when talking to mirrored DS servers, it does the Write and Commit
>> RPCs to the mirrors serially. This works, but is inefficient w.r.t. elapsed
>> to to
>> To do them concurrently, I need separate kernel processes/threads to do them.
>> I can think of two ways to do this:
>> 1 - The code that I have running in projects/pnfs-planb-server for the pNFS
>> side does a kproc_create() to create a kernel process that does the
>> RPC and
>> then krpc_exit()s.
>> - This was easy to code and works. However, I am concerned that there
>> going to be excessive overheads from doing all the kproc_create()s
>> Anyone know if these calls will result in large overheads?
>> 2 - I haven't coded this, but the other way I can think of to do this is to
>> create a pool of threads (kthread_create() is sufficient in this case,
>> think?) and then hand each RPC to an available thread so it can do the
>> - Other than a little more complex coding, the main issue I see with
>> this one
>> is "How many threads and when to create more/less of them.".
>> Anyhow, any comments w.r.t. the merits of either of the above approaches
>> (or a suggestion of other ways to do this) would be appreciated, rick
>taskqueue(9) is an existing mechanism to enqueue functions to execute
>asynch using a pool of threads, but it doesn't answer the scalability
>questions. In fact it may make them harder, inasmuch as I don't think
>there's a mechanism to dynamically adjust the number of threads after
>first calling taskqueue_start_threads().
Hmm, yes. Thanks for the pointer. I hadn't read "man taskqueue" until now.
The kernel RPC doesn't use this and I suspect that it is because of what you
said w.r.t. dynamically adjusting the # of threads.
However, it does save "hand coding" the queues for #2 and I'm lazy (plus
don't believe reinventing the wheel is the best plan).
I think I will try using taskqueue and just have a sysctl for #of-threads.
(Actually most of the code ends up the same, because basically they all
end up with a function with a single argument that does the RPC. The
only difference is what call starts the RPC.)
Anyone else have comments? rick
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