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

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Date:   Sat, 1 Feb 2020 11:51:52 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Martin T <m4rtntns@...il.com>
Subject: Re: Why is NIC driver queue depth driver dependent when it allocates
 system memory?

On Sat, Feb 1, 2020 at 11:14 AM Michal Kubecek <mkubecek@...e.cz> wrote:
>
> 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.

Ah, sorry for reading it too quickly.

Thanks.