What module is the i/o scheduler
At this point I have no need to modify the schedulers though that may change. Presently, my endeavor is to understand them. I've done a fair amount of reading on the subject from a variety of sources: wikipedia, Linux Kernel Development 2nd edition (ch. 10), Linux Driver Development 3rd edition (ch. 13) and a handful of others. I've got a fair understanding of the 4 main schedulers and how they work. However, I'm not yet sure of what they are.
From the code, eg block/noop-iosched.c, it appears to be a kernel module. But, when I do lsmod I don't see anything that jumps out as being the schedulers: eg nothing is named noop or cfq. Further, I don't see anything like
<scheduler> <size> <used> scsi_transport_sas
Which is what I would expect to have seen since it is the SAS transport which dequeues the requests from the request queue and hands them to the LLD. At least, I'm assuming I should see something like this because I see this output from lsmod with respect to my LLD:
scsi_transport_sas 35652 1 mpt3sas
This mid-layer driver, scsi_transport_sas, is used by mpt3sas my actual SAS controller. Since the mid-layer driver dequeues for the device, I'm just assuming that some similar relationship would be present between the mid-layer and the I/O scheduler.
So, my question is, what are the schedulers? Are they modules? Are they integrated components of the kernel? Are they software libraries and expose the correct functionality and are compiled with the other storage stack drivers? The references of I've mentioned earlier are great at explaining the work they do and how block drivers interact with them, but they didn't exactly say what they are.
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