Thanks for the response Mike. On Mon, 2009-04-06 at 10:43 -0500, Mike Christie wrote: > Chandra Seetharaman wrote: > > Hello All, > > > > During testing with the latest SCSI DH Handler on a rdac storage, Babu > > found that the failover time with 100+ luns takes about 15 minutes, > > which is not good. > > > > We found that the problem is due to the fact that we serialize activate > > in dm on the work queue. > > > > I thought we talked about this during the review? Yes, we did and the results were compared to the virgin code (w.r.t rdac handler) and the results were good (also I used only 49 luns) : http://marc.info/?l=dm-devel&m=120889858019762&w=2 > > > We can solve the problem in rdac handler in 2 ways > > 1. batch up the activates (mode_selects) and send few of them. > > 2. Do mode selects in async mode. > > I think most of the ugliness in the original async mode was due to > trying to use the REQ_BLOCK* path. With the scsi_dh_activate path, it > should now be easier because in the send path we do not have to worry > about queue locks being held and context. > little confused... we still are using REQ_TYPE_BLOCK_PC > I think we could just use blk_execute_rq_nowait to send the IO. Then we > would have a workqueue/thread per something (maybe per dh module I > thought), that would be queued/notified when the IO completed. The > thread could then process the IO and handle the next stage if needed. > > Why use the thread you might wonder? I think it fixes another issue with > the original async mode, and makes it easier if the scsi_dh module has can you elaborate the issue ? > to send more IO. When using the thread it would not have to worry about > the queue_lock being held in the IO completion path and does not have to > worry about being run from more restrictive contexts. You think queue_lock contention is an issue ? I agree with the restrictive context issue though. So, your suggestion is to move everything to async ? > > > > > > Just wondering if anybody had seen the same problem in other storages > > (EMC, HP and Alua). > > They should all have the same problem. > > > > > > Please share your experiences, so we can come up with a solution that > > works for all hardware handlers. > > > > regards, > > > > chandra > > > > -- > > dm-devel mailing list > > dm-devel@xxxxxxxxxx > > https://www.redhat.com/mailman/listinfo/dm-devel > -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
