netdev - Re: [PATCH rdma-next 0/4] Allow relaxed ordering read in VFs and VMs

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Date:   Tue, 11 Apr 2023 17:09:12 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Avihai Horon <avihaih@...dia.com>, Aya Levin <ayal@...dia.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, Meir Lichtinger <meirl@...lanox.com>,
        Michael Guralnik <michaelgur@...lanox.com>,
        netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Shay Drory <shayd@...dia.com>
Subject: Re: [PATCH rdma-next 0/4] Allow relaxed ordering read in VFs and VMs

On Tue, Apr 11, 2023 at 11:01:03AM -0300, Jason Gunthorpe wrote:
> On Mon, Apr 10, 2023 at 04:07:49PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> > 
> > From Avihai,
> > 
> > Currently, Relaxed Ordering (RO) can't be used in VFs directly and in
> > VFs assigned to QEMU, even if the PF supports RO. This is due to issues
> > in reporting/emulation of PCI config space RO bit and due to current
> > HCA capability behavior.
> > 
> > This series fixes it by using a new HCA capability and by relying on FW
> > to do the "right thing" according to the PF's PCI config space RO value.
> > 
> > Allowing RO in VFs and VMs is valuable since it can greatly improve
> > performance on some setups. For example, testing throughput of a VF on
> > an AMD EPYC 7763 and ConnectX-6 Dx setup showed roughly 60% performance
> > improvement.
> > 
> > Thanks
> > 
> > Avihai Horon (4):
> >   RDMA/mlx5: Remove pcie_relaxed_ordering_enabled() check for RO write
> >   RDMA/mlx5: Check pcie_relaxed_ordering_enabled() in UMR
> >   net/mlx5: Update relaxed ordering read HCA capabilities
> >   RDMA/mlx5: Allow relaxed ordering read in VFs and VMs
> 
> This looks OK, but the patch structure is pretty confusing.
> 
> It seems to me there are really only two patches here, the first is to
> add some static inline

I asked from Avihai to align all pcie_relaxed_ordering_enabled() calls
to be relevant for RO only. This is how we came to first two patches.

Thanks

> 
> 'mlx5 supports read ro'
> 
> which supports both the cap bits described in
> the PRM, with a little comment to explain that old devices only set
> the old cap.
> 
> And a second patch to call it in all the places we need to check before
> setting the mkc ro read bit.
> 
> Maybe a final third patch to sort out that mistake in the write side.
> 
> But this really doesn't have anything to do with VFs and VMs, this is
> adjusting the code to follow the current PRM because the old one was
> mis-desgined.
> 
> Jason