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SubjectRe: kthread vs. dm-daemon
Christophe Saout wrote:
> Am So, den 15.02.2004 schrieb Mike Christie um 23:13:
>
>
>>>Making dm-daemon use the kthread primitives would make dm-daemon a very
>>>small and stupid wrapper. Changing all dm targets to handle worker
>>>thread notification themselves would result in unnecessary code
>>>duplication.
>>
>>When dm-multipath is more stable it could be using a work queue (my
>>patch was prematurely sent). Imagine a large number of dm-mp devices
>>multipathing across two fabrics and one switch failing. Every dm-mp
>>device could be resubmitting io at the same time.
>
>
> I've thought of workqueues but at least for the snapshot and crypt
> target they're overkill.

It is a bigger problem for targets submitting io becuase the underlying
device's queue could hit nr_requests.

>
>>If every write for every dm-raid1 device is going through
>>a single dm-daemon, it could become a bottleneck.
>
>
> Hmm. The read decryption in dm-crypt is also a only-one-cpu-at-a-time
> thing. Didn't anybody notice that? Cryptoloop has the same limitation.
> I don't know how that could be handled differently. Every successful
> read gets dispatched to the next free cpu and decrypted?

You do not have to create a work_struct for every read. Why not just
have a bio-successful-reads-queue and a workstruct per device? That way
you can at least have num cpu devices running in parallel.
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