netdev - Re: [PATCH net-next 1/3] net: stmmac: Fix NAPI poll in TX path when in multi-queue

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Date:   Fri, 15 Feb 2019 16:35:57 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jose Abreu <jose.abreu@...opsys.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     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 1/3] net: stmmac: Fix NAPI poll in TX path when
 in multi-queue

On 2/15/19 5:42 AM, Jose Abreu wrote:
> Commit 8fce33317023 introduced the concept of NAPI per-channel and
> independent cleaning of TX path.
> 
> This is currently breaking performance in some cases. The scenario
> happens when all packets are being received in Queue 0 but the TX is
> performed in Queue != 0.
> 
> Fix this by using different NAPI instances per each TX and RX queue, as
> suggested by Florian.
> 
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>
> Cc: Florian Fainelli <f.fainelli@...il.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>
> ---

[snip]

> -	if (work_done < budget && napi_complete_done(napi, work_done)) {
> -		int stat;
> +	priv->xstats.napi_poll++;
>  
> +	work_done = stmmac_tx_clean(priv, budget, chan);
> +	if (work_done < budget && napi_complete_done(napi, work_done))

You should not be bounding your TX queue against the NAPI budge, it
should run unbound and clean as much as it can, which could be the
entire ring size if that is how many packets you pushed between
interrupts. That could be the cause of poor performance as well.
-- 
Florian