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>

Author: michich

drivers/net/ethernet/intel/ice/ice_common.c

@@ -1992,19 +1992,19 @@ ice_acquire_res(struct ice_hw *hw, enum ice_aq_res_ids res,
  */
 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));
 }
 
 /**

drivers/net/ethernet/intel/ice/ice_controlq.c

@@ -964,7 +964,7 @@ ice_sq_send_cmd(struct ice_hw *hw, struct ice_ctl_q_info *cq,
 	struct ice_aq_desc *desc_on_ring;
 	bool cmd_completed = false;
 	struct ice_sq_cd *details;
-	u32 total_delay = 0;
+	unsigned long timeout;
 	int status = 0;
 	u16 retval = 0;
 	u32 val = 0;
@@ -1057,13 +1057,14 @@ ice_sq_send_cmd(struct ice_hw *hw, struct ice_ctl_q_info *cq,
 		cq->sq.next_to_use = 0;
 	wr32(hw, cq->sq.tail, cq->sq.next_to_use);
 
+	timeout = jiffies + ICE_CTL_Q_SQ_CMD_TIMEOUT;
 	do {
 		if (ice_sq_done(hw, cq))
 			break;
 
-		udelay(ICE_CTL_Q_SQ_CMD_USEC);
-		total_delay++;
-	} while (total_delay < ICE_CTL_Q_SQ_CMD_TIMEOUT);
+		usleep_range(ICE_CTL_Q_SQ_CMD_USEC,
+			     ICE_CTL_Q_SQ_CMD_USEC * 3 / 2);
+	} while (time_before(jiffies, timeout));
 
 	/* if ready, copy the desc back to temp */
 	if (ice_sq_done(hw, cq)) {

drivers/net/ethernet/intel/ice/ice_controlq.h

@@ -34,7 +34,7 @@ enum ice_ctl_q {
 };
 
 /* Control Queue timeout settings - max delay 1s */
-#define ICE_CTL_Q_SQ_CMD_TIMEOUT	10000 /* Count 10000 times */
+#define ICE_CTL_Q_SQ_CMD_TIMEOUT	HZ    /* Wait max 1s */
 #define ICE_CTL_Q_SQ_CMD_USEC		100   /* Check every 100usec */
 #define ICE_CTL_Q_ADMIN_INIT_TIMEOUT	10    /* Count 10 times */
 #define ICE_CTL_Q_ADMIN_INIT_MSEC	100   /* Check every 100msec */