Subject: Re: [PATCH net-next 2/4] ice: sleep, don't busy-wait, for sq_cmd_timeout

From: Simon Horman <[email-masked]>
Date: Sun, 2 Apr 2023 13:18:11 +0200

On Sat, Apr 01, 2023 at 07:26:57PM +0200, Michal Schmidt wrote:
> 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 cq->sq_cmd_timeout in jiffies.
> 
> The sq_cmd_timeout is referenced 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 saw a report of high CPU usage with ptp4l where the busy-waiting in
> ice_sq_send_cmd dominated the profile. The patch should help with that.
> 
> Signed-off-by: Michal Schmidt <[email-masked]>
> ---
>  drivers/net/ethernet/intel/ice/ice_common.c   | 14 +++++++-------
>  drivers/net/ethernet/intel/ice/ice_controlq.c |  9 +++++----
>  drivers/net/ethernet/intel/ice/ice_controlq.h |  2 +-
>  3 files changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_common.c b/drivers/net/ethernet/intel/ice/ice_common.c
> index c2fda4fa4188..14cffe49fa8c 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(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 < hw->adminq.sq_cmd_timeout)) {
> -		mdelay(1);
> +	timeout = jiffies + 10 * hw->adminq.sq_cmd_timeout;

Not needed for this series. But it occurs to me that a clean-up would be to
use ICE_CTL_Q_SQ_CMD_TIMEOUT directly and remove the sq_cmd_timeout field,
as it seems to be only set to that constant.

> +	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));
>  }
>  
>  /**
> diff --git a/drivers/net/ethernet/intel/ice/ice_controlq.c b/drivers/net/ethernet/intel/ice/ice_controlq.c
> index 6bcfee295991..10125e8aa555 100644
> --- a/drivers/net/ethernet/intel/ice/ice_controlq.c
> +++ b/drivers/net/ethernet/intel/ice/ice_controlq.c
> @@ -967,7 +967,7 @@ 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;
> @@ -1060,13 +1060,14 @@ 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 + cq->sq_cmd_timeout;
>  	do {
>  		if (ice_sq_done(hw, cq))
>  			break;
>  
> -		udelay(ICE_CTL_Q_SQ_CMD_USEC);
> -		total_delay++;
> -	} while (total_delay < cq->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)) {
> diff --git a/drivers/net/ethernet/intel/ice/ice_controlq.h b/drivers/net/ethernet/intel/ice/ice_controlq.h
> index c07e9cc9fc6e..f2d3b115ae0b 100644
> --- a/drivers/net/ethernet/intel/ice/ice_controlq.h
> +++ b/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 */
> -- 
> 2.39.2
>