netdev - Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before prod db updating

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Date:   Wed, 24 Jan 2018 19:55:43 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     junxiao.bi@...cle.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before
 prod db updating

On Thu, 2018-01-25 at 11:27 +0800, jianchao.wang wrote:
> Hi Tariq
> 
> On 01/22/2018 10:12 AM, jianchao.wang wrote:
> > > > On 19/01/2018 5:49 PM, Eric Dumazet wrote:
> > > > > On Fri, 2018-01-19 at 23:16 +0800, jianchao.wang wrote:
> > > > > > Hi Tariq
> > > > > > 
> > > > > > Very sad that the crash was reproduced again after applied the patch.
> > > 
> > > Memory barriers vary for different Archs, can you please share more details regarding arch and repro steps?
> > The hardware is HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 12/27/2015
> > The xen is installed. The crash occurred in DOM0.
> > Regarding to the repro steps, it is a customer's test which does heavy disk I/O over NFS storage without any guest.
> > 
> 
> What is the finial suggestion on this ?
> If use wmb there, is the performance pulled down ?

Since https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=dad42c3038a59d27fced28ee4ec1d4a891b28155

we batch allocations, so mlx4_en_refill_rx_buffers() is not called that often.

I doubt the additional wmb() will have serious impact there.