netdev - Re: Why is NIC driver queue depth driver dependent when it allocates system memory?

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Date:   Sat, 1 Feb 2020 11:08:37 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Martin T <m4rtntns@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Why is NIC driver queue depth driver dependent when it allocates
 system memory?

On Thu, Jan 30, 2020 at 5:03 AM Martin T <m4rtntns@...il.com> wrote:
>
> Hi,
>
> when I read the source code of for example tg3 driver or e1000e
> driver, then looks like the driver queue is allocated from system
> memory. For example, in e1000_ethtool.c kcalloc() is called to
> allocate GFP_KERNEL memory.
>
> If system memory is allocated, then why are there driver-dependent
> limits? For example, in my workstation the maximum RX/TX queue for the
> NIC using tg3 driver is 511 while maximum RX/TX queue for the NIC
> using e1000e driver is 4096:

I doubt memory is a consideration for driver to decide the number
of queues. How many CPU's do you have? At least mellanox driver
uses the number of CPU's to determine the default value. Anyway,
you can change it to whatever you prefer.

Thanks.