netdev - Re: [PATCH net-next 06/11] bnxt_en: Improve -ENOMEM logic in NAPI poll loop.

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Message-ID: <20170828190504.jdlbyemn5xvmalsr@kafai-mba.dhcp.thefacebook.com>
Date:   Mon, 28 Aug 2017 12:05:04 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Michael Chan <michael.chan@...adcom.com>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 06/11] bnxt_en: Improve -ENOMEM logic in NAPI
 poll loop.

On Mon, Aug 28, 2017 at 01:40:30PM -0400, Michael Chan wrote:
> If we cannot allocate RX buffers in the NAPI poll loop when processing
> an RX event, the current code does not count that event towards the NAPI
> budget.  This can cause us to potentially loop forever in NAPI if we
> consistently cannot allocate new buffers.  Improve it by counting
> -ENOMEM event as 1 towards the NAPI budget.
>
> Cc: Martin KaFai Lau <kafai@...com>
> Signed-off-by: Michael Chan <michael.chan@...adcom.com>
Thanks for fixing it.

Reported-by: Martin KaFai Lau <kafai@...com>
Acked-by: Martin KaFai Lau <kafai@...com>

> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 1afb408..a34fcdd 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> @@ -1850,6 +1850,13 @@ static int bnxt_poll_work(struct bnxt *bp, struct bnxt_napi *bnapi, int budget)
>  							   &event);
>  			if (likely(rc >= 0))
>  				rx_pkts += rc;
> +			/* Increment rx_pkts when rc is -ENOMEM to count towards
> +			 * the NAPI budget.  Otherwise, we may potentially loop
> +			 * here forever if we consistently cannot allocate
> +			 * buffers.
> +			 */
> +			else if (rc == -ENOMEM)
> +				rx_pkts++;
>  			else if (rc == -EBUSY)	/* partial completion */
>  				break;
>  		} else if (unlikely((TX_CMP_TYPE(txcmp) ==
> --
> 1.8.3.1
>