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

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Date:   Thu, 30 Jan 2020 08:56:29 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin T <m4rtntns@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: Why is NIC driver queue depth driver dependent when it
 allocates system memory?

On Thu, 30 Jan 2020 15:02:02 +0200, Martin T 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:

Hi Martin,

the idea is that drivers can choose the initial setting which are
optimal for the implementation and the hardware. Whether they actually
are, or whether values chosen 10 years ago for tg3 and e1000e are
reasonable for modern uses of that hardware could perhaps be questioned.