[SCSI] isci: dynamic interrupt coalescing
Hardware allows both an outstanding number commands and a timeout value
(whichever occurs first) as a gate to the next interrupt generation. This
scheme at completion time looks at the remaining number of outstanding tasks
and sets the timeout to maximize small transaction operation. If transactions
are large (take more than a few 10s of microseconds to complete) then
performance is not interrupt processing bound, so the small timeouts this
scheme generates are overridden by the time it takes for a completion to
arrive.
Tested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
diff --git a/drivers/scsi/isci/host.c b/drivers/scsi/isci/host.c
index 26072f1..2328f98 100644
--- a/drivers/scsi/isci/host.c
+++ b/drivers/scsi/isci/host.c
@@ -1091,6 +1091,7 @@
struct isci_request *request;
struct isci_request *next_request;
struct sas_task *task;
+ u16 active;
INIT_LIST_HEAD(&completed_request_list);
INIT_LIST_HEAD(&errored_request_list);
@@ -1181,6 +1182,13 @@
}
}
+ /* the coalesence timeout doubles at each encoding step, so
+ * update it based on the ilog2 value of the outstanding requests
+ */
+ active = isci_tci_active(ihost);
+ writel(SMU_ICC_GEN_VAL(NUMBER, active) |
+ SMU_ICC_GEN_VAL(TIMER, ISCI_COALESCE_BASE + ilog2(active)),
+ &ihost->smu_registers->interrupt_coalesce_control);
}
/**
@@ -1471,7 +1479,7 @@
struct isci_host *ihost = container_of(sm, typeof(*ihost), sm);
/* set the default interrupt coalescence number and timeout value. */
- sci_controller_set_interrupt_coalescence(ihost, 0x10, 250);
+ sci_controller_set_interrupt_coalescence(ihost, 0, 0);
}
static void sci_controller_ready_state_exit(struct sci_base_state_machine *sm)