linux-kernel - Re: [net-next v4 2/2] tg3: Link queues to NAPIs

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Message-ID: <CACKFLimL=x_KQeyOy_2FLcew=TFD0MjvKJbH_BaydCEG_Oa0Cw@mail.gmail.com>
Date: Wed, 9 Oct 2024 15:36:59 -0700
From: Michael Chan <michael.chan@...adcom.com>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, pavan.chebbi@...adcom.com, 
	Michael Chan <mchan@...adcom.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [net-next v4 2/2] tg3: Link queues to NAPIs

On Wed, Oct 9, 2024 at 10:55 AM Joe Damato <jdamato@...tly.com> wrote:
>
> Link queues to NAPIs using the netdev-genl API so this information is
> queryable.
>
> First, test with the default setting on my tg3 NIC at boot with 1 TX
> queue:
>
> $ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>                          --dump queue-get --json='{"ifindex": 2}'
>
> [{'id': 0, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8195, 'type': 'rx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8196, 'type': 'rx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8197, 'type': 'rx'},
>  {'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'tx'}]
>

This is correct.  When TSS is not enabled (1 TX ring only), the TX
ring uses NAPI 0 and the RSS RX rings use NAPI 1, 2, 3, 4.

> Now, adjust the number of TX queues to be 4 via ethtool:
>
> $ sudo ethtool -L eth0 tx 4
> $ sudo ethtool -l eth0 | tail -5
> Current hardware settings:
> RX:             4
> TX:             4
> Other:          n/a
> Combined:       n/a
>
> Despite "Combined: n/a" in the ethtool output, /proc/interrupts shows
> the tg3 has renamed the IRQs to be combined:
>
> 343: [...] eth0-0
> 344: [...] eth0-txrx-1
> 345: [...] eth0-txrx-2
> 346: [...] eth0-txrx-3
> 347: [...] eth0-txrx-4
>
> Now query this via netlink to ensure the queues are linked properly to
> their NAPIs:
>
> $ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>                          --dump queue-get --json='{"ifindex": 2}'
> [{'id': 0, 'ifindex': 2, 'napi-id': 8960, 'type': 'rx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8961, 'type': 'rx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8962, 'type': 'rx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8963, 'type': 'rx'},
>  {'id': 0, 'ifindex': 2, 'napi-id': 8960, 'type': 'tx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8961, 'type': 'tx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8962, 'type': 'tx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8963, 'type': 'tx'}]
>

This is also correct after reviewing the driver code.  When TSS is
enabled, NAPI 0 is no longer used for any TX ring.  All TSS and RSS
rings start from NAPI 1.  NAPI 0 is only used for link change and
other error interrupts.

> As you can see above, id 0 for both TX and RX share a NAPI, NAPI ID
> 8960, and so on for each queue index up to 3.
>
> Signed-off-by: Joe Damato <jdamato@...tly.com>

Thanks.
Reviewed-by: Michael Chan <michael.chan@...adcom.com>

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