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authorKiyoshi Ueda <k-ueda@ct.jp.nec.com>2009-06-22 10:12:37 +0100
committerAlasdair G Kergon <agk@redhat.com>2009-06-22 10:12:37 +0100
commitf40c67f0f7e2767f80f7cbcbc1ab86c4113c202e (patch)
treee8a20f3ceac54ac6edd0f25ffa95c0216a949c52 /arch
parent523d9297d43cce3fa6de6474b7674329e98743b1 (diff)
dm mpath: change to be request based
This patch converts dm-multipath target to request-based from bio-based. Basically, the patch just converts the I/O unit from struct bio to struct request. In the course of the conversion, it also changes the I/O queueing mechanism. The change in the I/O queueing is described in details as follows. I/O queueing mechanism change ----------------------------- In I/O submission, map_io(), there is no mechanism change from bio-based, since the clone request is ready for retry as it is. However, in I/O complition, do_end_io(), there is a mechanism change from bio-based, since the clone request is not ready for retry. In do_end_io() of bio-based, the clone bio has all needed memory for resubmission. So the target driver can queue it and resubmit it later without memory allocations. The mechanism has almost no overhead. On the other hand, in do_end_io() of request-based, the clone request doesn't have clone bios, so the target driver can't resubmit it as it is. To resubmit the clone request, memory allocation for clone bios is needed, and it takes some overheads. To avoid the overheads just for queueing, the target driver doesn't queue the clone request inside itself. Instead, the target driver asks dm core for queueing and remapping the original request of the clone request, since the overhead for queueing is just a freeing memory for the clone request. As a result, the target driver doesn't need to record/restore the information of the original request for resubmitting the clone request. So dm_bio_details in dm_mpath_io is removed. multipath_busy() --------------------- The target driver returns "busy", only when the following case: o The target driver will map I/Os, if map() function is called and o The mapped I/Os will wait on underlying device's queue due to their congestions, if map() function is called now. In other cases, the target driver doesn't return "busy". Otherwise, dm core will keep the I/Os and the target driver can't do what it wants. (e.g. the target driver can't map I/Os now, so wants to kill I/Os.) Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Acked-by: Hannes Reinecke <hare@suse.de> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'arch')
0 files changed, 0 insertions, 0 deletions