netdev - Re: [PATCH net-next v2] net: airoha: Implement BQL support

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Message-ID: <Zw6ZyoJCv0_EOnpf@lore-desk>
Date: Tue, 15 Oct 2024 18:35:22 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Felix Fietkau <nbd@....name>, Sean Wang <sean.wang@...iatek.com>,
	Mark Lee <Mark-MC.Lee@...iatek.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org,
	upstream@...oha.com
Subject: Re: [PATCH net-next v2] net: airoha: Implement BQL support

> On Tue, 15 Oct 2024 17:54:59 +0200 Lorenzo Bianconi wrote:
> > > Oh, thought its called on stop. In that case we're probably good
> > > from BQL perspective.
> > > 
> > > But does it mean potentially very stale packets can sit on the Tx
> > > ring when the device is stopped, until it's started again?  
> > 
> > Do you mean the packets that the stack is transmitting when the .ndo_stop()
> > is run?
> 
> Whatever is in the queue at the time ndo_stop() gets called.
> Could be the full descriptor ring I presume?
> 
> > In airoha_dev_stop() we call netif_tx_disable() to disable the transmission
> > on new packets and inflight packets will be consumed by the completion napi,
> > is it not enough?
> 
> They will only get consumed if the DMA gets to them right?
> Stop seems to stop the DMA.
> 
> > I guess we can even add netdev_tx_reset_subqueue() for all netdev
> > queues in airoha_dev_stop(), I do not have a strong opinion about it. What
> > do you prefer?
> 
> So to be clear I think this patch is correct as of the current driver
> code. I'm just wondering if we should call airoha_qdma_cleanup_tx_queue()
> on stop as well, and then that should come with the reset.
> I think having a packet stuck in a queue may lead to all sort of oddness
> so my recommendation would be to flush the queues.

ack, I will post a fix for this. Do you prefer to resend even this patch? Up to you.

Regards,
Lorenzo

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