ice: sleep, don't busy-wait, for ICE_CTL_Q_SQ_CMD_TIMEOUT

The driver polls for ice_sq_done() with a 100 µs period for up to 1 s
and it uses udelay to do that.

Let's use usleep_range instead. We know sleeping is allowed here,
because we're holding a mutex (cq->sq_lock). To preserve the total
max waiting time, measure the timeout in jiffies.

ICE_CTL_Q_SQ_CMD_TIMEOUT is used also in ice_release_res(), but there
the polling period is 1 ms (i.e. 10 times longer). Since the timeout was
expressed in terms of the number of loops, the total timeout in this
function is 10 s. I do not know if this is intentional. This patch keeps
it.

The patch lowers the CPU usage of the ice-gnss-<dev_name> kernel thread
on my system from ~8 % to less than 1 %.

I received a report of high CPU usage with ptp4l where the busy-waiting
in ice_sq_send_cmd dominated the profile. This patch has been tested in
that usecase too and it made a huge improvement there.

Tested-by: Brent Rowsell <browsell@redhat.com>
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Sunitha Mekala <sunithax.d.mekala@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/net/ethernet/intel/ice/ice_common.c b/drivers/net/ethernet/intel/ice/ice_common.c
index f4c256563248..3638598d732b 100644
--- a/drivers/net/ethernet/intel/ice/ice_common.c
+++ b/drivers/net/ethernet/intel/ice/ice_common.c
@@ -1992,19 +1992,19 @@ ice_acquire_res_exit:
  */
 void ice_release_res(struct ice_hw *hw, enum ice_aq_res_ids res)
 {
-	u32 total_delay = 0;
+	unsigned long timeout;
 	int status;
 
-	status = ice_aq_release_res(hw, res, 0, NULL);
-
 	/* there are some rare cases when trying to release the resource
 	 * results in an admin queue timeout, so handle them correctly
 	 */
-	while ((status == -EIO) && (total_delay < ICE_CTL_Q_SQ_CMD_TIMEOUT)) {
-		mdelay(1);
+	timeout = jiffies + 10 * ICE_CTL_Q_SQ_CMD_TIMEOUT;
+	do {
 		status = ice_aq_release_res(hw, res, 0, NULL);
-		total_delay++;
-	}
+		if (status != -EIO)
+			break;
+		usleep_range(1000, 2000);
+	} while (time_before(jiffies, timeout));
 }
 
 /**