From: David Ahern <dsahern@gmail.com>
To: Saeed Mahameed <saeedm@mellanox.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: max channels for mlx5
Date: Mon, 4 May 2020 17:04:21 -0600 [thread overview]
Message-ID: <f11d1ff2-b16b-37d3-0e17-4a051c29a9b5@gmail.com> (raw)
In-Reply-To: <2f5110e579a21737e5c13b23482eff6fdb6f3808.camel@mellanox.com>
On 5/4/20 3:46 PM, Saeed Mahameed wrote:
> what is the amount of msix avaiable for eth0 port ?
>
> businfo=$(ethtool -i eth0 | grep bus-info | cut -d":" -f2-)
> cat /proc/interrupts | grep $businfo | wc -l
64
>
> So if number of msix is 64, we can only use 63 for data path
> completions ..
>
> do you have sriov enabled ?
no
>
> what is the FW version you have ?
$ ethtool -i eth0
driver: mlx5_core
version: 5.0-0
firmware-version: 14.27.1016 (MT_2420110034)
> we need to figure out if this is a system MSIX limitation or a FW
> limitation.
>
>> A side effect of this limit is XDP_REDIRECT drops packets if a vhost
>> thread gets scheduled on cpus 64 and up since the tx queue is based
>> on
>> processor id:
>>
>> int mlx5e_xdp_xmit(struct net_device *dev, int n, struct xdp_frame
>> **frames,
>> u32 flags)
>> {
>> ...
>> sq_num = smp_processor_id();
>> if (unlikely(sq_num >= priv->channels.num))
>> return -ENXIO;
>>
>> So in my example if the redirect happens on cpus 64-95, which is 1/3
>> of
>> my hardware threads, the packet is just dropped.
>>
>
> Know XDP redirect issue, you need to tune the RSS and affinity on RX
> side and match TX count and affinity on TX side, so you won't end up on
> a wrong CPU on the TX side
Understood for port to port redirect.
This use case is a virtual machine with a tap device + vhost bypassing
host kernel stack and redirecting to a port. Losing a third of the cpus
for vhost threads is a huge limitation.
prev parent reply other threads:[~2020-05-04 23:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-04 0:41 max channels for mlx5 David Ahern
2020-05-04 21:46 ` Saeed Mahameed
2020-05-04 23:04 ` David Ahern [this message]
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