netdev - Re: [net-next 10/10] net/mlx5e: Add support for PCI relaxed ordering

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Message-ID: <20200706095217.55c34281@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 6 Jul 2020 09:52:17 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Aya Levin <ayal@...lanox.com>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "helgaas@...nel.org" <helgaas@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        "alexander.h.duyck@...ux.intel.com\"" 
        <alexander.h.duyck@...ux.intel.com>
Subject: Re: [net-next 10/10] net/mlx5e: Add support for PCI relaxed
 ordering

On Mon, 6 Jul 2020 16:00:59 +0300 Aya Levin wrote:
> Assuming the discussions with Bjorn will conclude in a well-trusted API 
> that ensures relaxed ordering in enabled, I'd still like a method to 
> turn off relaxed ordering for performance debugging sake.
> Bjorn highlighted the fact that the PCIe sub system can only offer a 
> query method. Even if theoretically a set API will be provided, this 
> will not fit a netdev debugging - I wonder if CPU vendors even support 
> relaxed ordering set/unset...
> On the driver's side relaxed ordering is an attribute of the mkey and 
> should be available for configuration (similar to number of CPU vs. 
> number of channels).
> Based on the above, and binding the driver's default relaxed ordering to 
> the return value from pcie_relaxed_ordering_enabled(), may I continue 
> with previous direction of a private-flag to control the client side (my 
> driver) ?

That's fine with me, chicken bit seems reasonable as long as the
default is dictated by the PCI subsystem. I have no particularly 
strong feeling on the API used for the chicken bit, but others may.