linux-kernel - Re: [PATCH V10 net-next 06/10] net: hibmcge: Implement .ndo_start

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Message-ID: <20240915171622.3ef8ff0e@kernel.org>
Date: Sun, 15 Sep 2024 17:16:22 +0200
From: Jakub Kicinski <kuba@...nel.org>
To: Jijie Shao <shaojijie@...wei.com>
Cc: <davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
 <shenjian15@...wei.com>, <wangpeiyang1@...wei.com>,
 <liuyonglong@...wei.com>, <chenhao418@...wei.com>,
 <sudongming1@...wei.com>, <xujunsheng@...wei.com>,
 <shiyongbang@...wei.com>, <libaihan@...wei.com>, <andrew@...n.ch>,
 <jdamato@...tly.com>, <horms@...nel.org>,
 <kalesh-anakkur.purayil@...adcom.com>, <jonathan.cameron@...wei.com>,
 <shameerali.kolothum.thodi@...wei.com>, <salil.mehta@...wei.com>,
 <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V10 net-next 06/10] net: hibmcge: Implement
 .ndo_start_xmit function

On Thu, 12 Sep 2024 10:51:23 +0800 Jijie Shao wrote:
> +static int hbg_napi_tx_recycle(struct napi_struct *napi, int budget)
> +{
> +	struct hbg_ring *ring = container_of(napi, struct hbg_ring, napi);
> +	/* This smp_load_acquire() pairs with smp_store_release() in
> +	 * hbg_start_xmit() called in xmit process.
> +	 */
> +	u32 ntu = smp_load_acquire(&ring->ntu);
> +	struct hbg_priv *priv = ring->priv;
> +	struct hbg_buffer *buffer;
> +	u32 ntc = ring->ntc;
> +	int packet_done = 0;
> +
> +	while (packet_done < budget) {

you should so some cleanup even if budget is 0
in fact you can hardcode the amount of work Tx NAPI does to 128 and
don't look at the budget as a limit. Per NAPI documentation budget
is for Rx

> +		if (unlikely(hbg_queue_is_empty(ntc, ntu, ring)))
> +			break;
> +
> +		/* make sure HW write desc complete */
> +		dma_rmb();
> +
> +		buffer = &ring->queue[ntc];
> +		if (buffer->state != HBG_TX_STATE_COMPLETE)
> +			break;
> +
> +		hbg_buffer_free(buffer);
> +		ntc = hbg_queue_next_prt(ntc, ring);
> +		packet_done++;
> +	}
> +
> +	/* This smp_store_release() pairs with smp_load_acquire() in
> +	 * hbg_start_xmit() called in xmit process.
> +	 */
> +	smp_store_release(&ring->ntc, ntc);
> +	netif_wake_queue(priv->netdev);
> +
> +	if (likely(napi_complete_done(napi, packet_done)))

if packet_done >= budget you should not call napi_complete_done()
as you are not done

> +		hbg_hw_irq_enable(priv, HBG_INT_MSK_TX_B, true);