Subject: Re: [PATCH net 2/2] pds_core: Add a retry mechanism when the adminq is full

From: Michal Swiatkowski <[email-masked]>
Date: Wed, 29 Jan 2025 09:08:46 +0100

On Tue, Jan 28, 2025 at 04:43:37PM -0800, Shannon Nelson wrote:
> From: Brett Creeley <[email-masked]>
> 
> If the adminq is full, the driver reports failure when trying to post
> new adminq commands. This is a bit aggressive and unexpected because
> technically the adminq post didn't fail in this case, it was just full.
> To harden this path add support for a bounded retry mechanism.
> 
> It's possible some commands take longer than expected, maybe hundreds
> of milliseconds or seconds due to other processing on the device side,
> so to further reduce the chance of failure due to adminq full increase
> the PDS_CORE_DEVCMD_TIMEOUT from 5 to 10 seconds.
> 
> The caller of pdsc_adminq_post() may still see -EAGAIN reported if the
> space in the adminq never freed up. In this case they can choose to
> call the function again or fail. For now, no callers will retry.
> 
> Fixes: 01ba61b55b20 ("pds_core: Add adminq processing and commands")
> Signed-off-by: Brett Creeley <[email-masked]>
> Signed-off-by: Shannon Nelson <[email-masked]>
> ---
>  drivers/net/ethernet/amd/pds_core/adminq.c | 22 ++++++++++++++++++----
>  include/linux/pds/pds_core_if.h            |  2 +-
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/amd/pds_core/adminq.c b/drivers/net/ethernet/amd/pds_core/adminq.c
> index c83a0a80d533..387de1712827 100644
> --- a/drivers/net/ethernet/amd/pds_core/adminq.c
> +++ b/drivers/net/ethernet/amd/pds_core/adminq.c
> @@ -181,7 +181,10 @@ static int __pdsc_adminq_post(struct pdsc *pdsc,
>  	else
>  		avail -= q->head_idx + 1;
>  	if (!avail) {
> -		ret = -ENOSPC;
> +		if (!pdsc_is_fw_running(pdsc))
> +			ret = -ENXIO;
> +		else
> +			ret = -EAGAIN;

Short if will fit nice here, anyway:
Reviewed-by: Michal Swiatkowski <[email-masked]>

>  		goto err_out_unlock;
>  	}
>  
> @@ -251,14 +254,25 @@ int pdsc_adminq_post(struct pdsc *pdsc,
>  	}
>  
>  	wc.qcq = &pdsc->adminqcq;
> -	index = __pdsc_adminq_post(pdsc, &pdsc->adminqcq, cmd, comp, &wc);
> +	time_start = jiffies;
> +	time_limit = time_start + HZ * pdsc->devcmd_timeout;
> +	do {
> +		index = __pdsc_adminq_post(pdsc, &pdsc->adminqcq, cmd, comp,
> +					   &wc);
> +		if (index != -EAGAIN)
> +			break;
> +
> +		dev_dbg(pdsc->dev, "Retrying adminq cmd opcode %u\n",
> +			cmd->opcode);
> +		/* Give completion processing a chance to free up space */
> +		msleep(1);
> +	} while (time_before(jiffies, time_limit));
> +
>  	if (index < 0) {
>  		err = index;
>  		goto err_out;
>  	}
>  
> -	time_start = jiffies;
> -	time_limit = time_start + HZ * pdsc->devcmd_timeout;
>  	do {
>  		/* Timeslice the actual wait to catch IO errors etc early */
>  		poll_jiffies = msecs_to_jiffies(poll_interval);
> diff --git a/include/linux/pds/pds_core_if.h b/include/linux/pds/pds_core_if.h
> index 17a87c1a55d7..babc6d573acd 100644
> --- a/include/linux/pds/pds_core_if.h
> +++ b/include/linux/pds/pds_core_if.h
> @@ -22,7 +22,7 @@
>  #define PDS_CORE_BAR0_INTR_CTRL_OFFSET		0x2000
>  #define PDS_CORE_DEV_CMD_DONE			0x00000001
>  
> -#define PDS_CORE_DEVCMD_TIMEOUT			5
> +#define PDS_CORE_DEVCMD_TIMEOUT			10
>  
>  #define PDS_CORE_CLIENT_ID			0
>  #define PDS_CORE_ASIC_TYPE_CAPRI		0
> -- 
> 2.17.1