linux-kernel - Re: [PATCH net-next v2 06/10] net: stmmac: Do not disable interrupts when cleaning TX

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Message-ID: <CA+FuTSc4MFfjBNpvN2hRh9_MRmxSYw2xY6wp32Hsbw0E=pqUdw@mail.gmail.com>
Date:   Fri, 28 Jun 2019 15:08:50 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>
Subject: Re: [PATCH net-next v2 06/10] net: stmmac: Do not disable interrupts
 when cleaning TX

On Fri, Jun 28, 2019 at 3:30 AM Jose Abreu <Jose.Abreu@...opsys.com> wrote:
>
> This is a performance killer and anyways the interrupts are being
> disabled by RX NAPI so no need to disable them again.

By the

        if ((status & handle_rx) && (chan < priv->plat->rx_queues_to_use)) {
                stmmac_disable_dma_irq(priv, priv->ioaddr, chan);
                napi_schedule_irqoff(&ch->rx_napi);
        }

branch directly above? If so, is it possible to have fewer rx than tx
queues and miss this?

this logic seems more complex than needed?

        if (status)
                status |= handle_rx | handle_tx;

        if ((status & handle_rx) && (chan < priv->plat->rx_queues_to_use)) {

        }

        if ((status & handle_tx) && (chan < priv->plat->tx_queues_to_use)) {

        }

status & handle_rx implies status & handle_tx and vice versa.


>
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>
> Cc: Joao Pinto <jpinto@...opsys.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
> Cc: Alexandre Torgue <alexandre.torgue@...com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 4a5941caaadc..e8f3e76889c8 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2061,10 +2061,8 @@ static int stmmac_napi_check(struct stmmac_priv *priv, u32 chan)
>                 napi_schedule_irqoff(&ch->rx_napi);
>         }
>
> -       if ((status & handle_tx) && (chan < priv->plat->tx_queues_to_use)) {
> -               stmmac_disable_dma_irq(priv, priv->ioaddr, chan);
> +       if ((status & handle_tx) && (chan < priv->plat->tx_queues_to_use))
>                 napi_schedule_irqoff(&ch->tx_napi);
> -       }
>
>         return status;
>  }
> @@ -3570,8 +3568,8 @@ static int stmmac_napi_poll_tx(struct napi_struct *napi, int budget)
>         work_done = stmmac_tx_clean(priv, DMA_TX_SIZE, chan);
>         work_done = min(work_done, budget);
>
> -       if (work_done < budget && napi_complete_done(napi, work_done))
> -               stmmac_enable_dma_irq(priv, priv->ioaddr, chan);
> +       if (work_done < budget)
> +               napi_complete_done(napi, work_done);

It does seem odd that stmmac_napi_poll_rx and stmmac_napi_poll_tx both
call stmmac_enable_dma_irq(..) independent of the other. Shouldn't the
IRQ remain masked while either is active or scheduled? That is almost
what this patch does, though not exactly.