Bart Van Assche <bvanassche@acm.org> says:
Hi Martin,
This patch series optimizes the hot path of the UFS driver by making
struct scsi_cmnd and struct ufshcd_lrb adjacent. Making these two data
structures adjacent is realized as follows:
@@ -9040,6 +9046,7 @@ static const struct scsi_host_template ufshcd_driver_template = {
.name = UFSHCD,
.proc_name = UFSHCD,
.map_queues = ufshcd_map_queues,
+ .cmd_size = sizeof(struct ufshcd_lrb),
.init_cmd_priv = ufshcd_init_cmd_priv,
.queuecommand = ufshcd_queuecommand,
.mq_poll = ufshcd_poll,
The following changes had to be made prior to making these two data
structures adjacent:
* Add support for driver-internal and reserved commands in the SCSI core.
* Instead of making the reserved command slot (hba->reserved_slot)
invisible to the SCSI core, let the SCSI core allocate a reserved command.
* Remove all UFS data structure members that are no longer needed
because struct scsi_cmnd and struct ufshcd_lrb are now adjacent
* Call ufshcd_init_lrb() from inside the code for queueing a command instead of
calling this function before I/O starts. This is necessary because
ufshcd_memory_alloc() allocates fewer instances than the block layer
allocates requests. See also the following code in the block layer
core:
if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
hctx->numa_node))
Although the UFS driver could be modified such that ufshcd_init_lrb()
is called from ufshcd_init_cmd_priv(), realizing this would require
moving the memory allocations that happen from inside
ufshcd_memory_alloc() into ufshcd_init_cmd_priv(). That would make
this patch series even larger. Although ufshcd_init_lrb() is called for each
command, the benefits of reduced indirection and better cache efficiency
outweigh the small overhead of per-command lrb initialization.
* ufshcd_add_scsi_host() happens now before any device management
commands are submitted. This change is necessary because this patch
makes device management command allocation happen when the SCSI host
is allocated.
* Allocate as many command slots as the host controller supports. Decrease
host->cmds_per_lun if necessary once it is clear whether or not the UFS
device supports less command slots than the host controller.
Please consider this patch series for the next merge window.
Thanks,
Bart.
Link: https://patch.msgid.link/20251031204029.2883185-1-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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