linux-kernel - Re: [PATCH net-next 0/4] net/mlx5: Memory optimizations

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Date:   Thu, 2 Dec 2021 18:55:37 +0000
From:   Saeed Mahameed <saeedm@...dia.com>
To:     Shay Drory <shayd@...dia.com>, "kuba@...nel.org" <kuba@...nel.org>
CC:     Jiri Pirko <jiri@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 0/4] net/mlx5: Memory optimizations

On Thu, 2021-12-02 at 09:31 -0800, Jakub Kicinski wrote:
> On Wed, 1 Dec 2021 10:22:17 +0200 Shay Drory wrote:
> > On 11/30/2021 21:39, Jakub Kicinski wrote:
> > > On Tue, 30 Nov 2021 17:07:02 +0200 Shay Drory wrote:  
> > > >   - Patch-1 Provides I/O EQ size resource which enables to save
> > > >     up to 128KB.
> > > >   - Patch-2 Provides event EQ size resource which enables to
> > > > save up to
> > > >     512KB.  
> > > Why is something allocated in host memory a device resource? 🤔  
> > 
> > EQ resides in the host memory. It is RO for host driver, RW by
> > device.
> > When interrupt is generated EQ entry is placed by device and read
> > by driver.
> > It indicates about what event occurred such as CQE, async and more.
> 
> I understand that. My point was the resource which is being consumed
> here is _host_ memory. Is there precedent for configuring host memory
> consumption via devlink resource?
> 

it's a device resource size nonetheless, devlink resource API makes
total sense.

> I'd even question whether this belongs in devlink in the first place.
> It is not global device config in any way. If devlink represents the
> entire device it's rather strange to have a case where main instance
> limits a size of some resource by VFs and other endpoints can still
> choose whatever they want.
> 

This resource is per function instance, we have devlink instance per
function, e.g. in the VM, there is a VF devlink instance the VM user
can use to control own VF resources. in the PF/Hypervisor, the only
devlink representation of the VF will be devlink port function (used
for other purposes)

for example:

A tenant can fine-tune a resource size tailored to their needs via the
VF's own devlink instance.

An admin can only control or restrict a max size of a resource for a
given port function ( the devlink instance that represents the VF in
the hypervisor). (note: this patchset is not about that)

> > > Did you analyze if others may need this?  
> > 
> > So far no feedback by other vendors.
> > The resources are implemented in generic way, if other vendors
> > would
> > like to implement them.
> 
> Well, I was hoping you'd look around, but maybe that's too much to
> ask
> of a vendor.

We looked, eq is a common object among many other drivers.
and DEVLINK_PARAM_GENERIC_ID_MAX_MACS is already a devlink generic
param, and i am sure other vendors have limited macs per VF :) .. 
so this applies to all vendors even if they don't advertise it.