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

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Message-ID: <20200201191441.GC23638@unicorn.suse.cz>
Date:   Sat, 1 Feb 2020 20:14:41 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>, Martin T <m4rtntns@...il.com>
Subject: Re: Why is NIC driver queue depth driver dependent when it allocates
 system memory?

On Sat, Feb 01, 2020 at 11:08:37AM -0800, Cong Wang wrote:
> 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.

Martin was asking about ring sizes, not about number of queues.

Michal