Messages in this thread |  | | Subject | Re: [PATCH 1/2] scsi_host: add support for request batching | From | Bart Van Assche <> | Date | Tue, 4 Jun 2019 15:40:18 -0700 |
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On 5/30/19 4:28 AM, Paolo Bonzini wrote: > This allows a list of requests to be issued, with the LLD only writing > the hardware doorbell when necessary, after the last request was prepared. > This is more efficient if we have lists of requests to issue, particularly > on virtualized hardware, where writing the doorbell is more expensive than > on real hardware. > > The use case for this is plugged IO, where blk-mq flushes a batch of > requests all at once. > > The API is the same as for blk-mq, just with blk-mq concepts tweaked to > fit the SCSI subsystem API: the "last" flag in blk_mq_queue_data becomes > a flag in scsi_cmnd, while the queue_num in the commit_rqs callback is > extracted from the hctx and passed as a parameter. > > The only complication is that blk-mq uses different plugging heuristics > depending on whether commit_rqs is present or not. So we have two > different sets of blk_mq_ops and pick one depending on whether the > scsi_host template uses commit_rqs or not.
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
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