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

[Tariq Toukan]

On 25/01/2018 8:25 AM, jianchao.wang wrote:
> Hi Eric
>
> Thanks for you kindly response and suggestion.
> That's really appreciated.
>
> Jianchao
>
> On 01/25/2018 11:55 AM, Eric Dumazet wrote:
> > 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 ?

I want to evaluate this effect.
I agree with Eric, expected impact is restricted, especially after 
batching the allocations.

> > Since https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_davem_net-2Dnext.git_commit_-3Fid-3Ddad42c3038a59d27fced28ee4ec1d4a891b28155&d=DwICaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26ATvfo6QSTvZyQ&m=c0oI8duFkyFBILMQYDsqRApHQrOlLY_2uGiz_utcd7s&s=E4_XKmSI0B63qB0DLQ1EX_fj1bOP78ZdeYADBf33B-k&e=
> >
> > we batch allocations, so mlx4_en_refill_rx_buffers() is not called that often.
> >
> > I doubt the additional wmb() will have serious impact there.

I will test the effect (it'll be beginning of next week).
I'll update so we can make a more confident decision.

Thanks,
Tariq

> >
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