Adding the linux-scsi list... -- mikem "If you don't read the newspaper, you are uninformed; if you do read the newspaper, you are misinformed." - Mark Twain > -----Original Message----- > From: scameron@xxxxxxxxxxxxxxxxxx [mailto:scameron@xxxxxxxxxxxxxxxxxx] > Sent: Thursday, November 03, 2011 8:47 AM > To: james.bottomley@xxxxxxxxxxxxxxxxxxxxx > Cc: Brace, Don; Miller, Mike (OS Dev); scameron@xxxxxxxxxxxxxxxxxx > Subject: Question about interface between scsi mid layer and lld > > > Hi James, > > I had a question about the interface between the scsi mid layer > and LLDs, esp. how commands are submitted to the LLD. Suppose you > have an HBA that might prefer to have a batch of commands submitted > to it all at once rather than one by one. > > With the block layer interface, the LLD has a function which the > block layer calls to begin submitting requests, but then this function > calls blk_peek_request() and blk_start_request to pull requests out > of the block layer, and so it could pull as many as it could hold, > or as many as the block layer had lying around for it to work on. > > The scsi LLD interface, with the queuecommand function is different > in that it gets called once for each SCSI command, and there's as far > as I know no way for the LLD to kind of pull more commands out of the > scsi mid layer. > > First, am I correct in thinking that there's no way for the LLD to > process more than one command per call to queuecommand? Or am > I missing some interface that's already there? > > Second, if I am correct, are there any plans to provide an interface > to do something like that? > > I'm thinking with the existing interface, if I want to batch commands > in SCSI a driver, I have to introduce latency, as the LLD has no idea > how many commands the mid layer has to submit, or when it will submit > them -- and introducing latency is probably not a good idea and likely > will eat all the benefits that might be gained by batching submissions > to the HBA. > > Thanks, > > -- steve > -- 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
