On Wed, 2012-05-16 at 11:54 -0400, Bernd Schubert wrote: > 2) Low SRP command queues. Is there a reason why > SRP_RQ_SHIFT/SRP_RQ_SIZE and their depend values such as SRP_RQ_SIZE are > so small? That's a decision that has been around since the beginning of the driver as far as I can tell. It looks to be a balance between device needs and memory usage, and it can certainly be raised -- I've run locally with SRP_RQ_SHIFT set to 7 (shost.can_queue 126) and I'm sure 8 would be no problem, either. I didn't see a performance improvement on my workload, but may you will. Because we take the minimum of our initiator queue depth and the initial credits from the target (each req consumes a credit), going higher than 8 doesn't buy us much, as I don't know off-hand of any target that gives out more than 256 credits. The memory used for the command ring will vary depending on the value of SRP_RQ_SHIFT and the number of s/g entries allows to be put in the command. 255 s/g entries requires an 8 KB allocation for each request (~4200 bytes), so we currently require 512 KB of buffers for the send queue for each target. Going to 8 will require 2 MB max per target, which probably isn't a real issue. There's also a response ring with an allocation size that depends on the target, but those should be pretty small buffers, say 1 KB * (1 << SRP_RQ_SHIFT). -- Dave Dillow National Center for Computational Science Oak Ridge National Laboratory (865) 241-6602 office -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
