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Date:   Thu, 1 Dec 2016 13:33:52 +0100
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Jisheng Zhang <jszhang@...vell.com>
Cc:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        Arnd Bergmann <arnd@...db.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dmitri Epshtein <dima@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>,
        Yelena Krivosheev <yelena@...vell.com>,
        Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v5 net-next 4/7] net: mvneta: Convert to be 64 bits compatible

Hi Jisheng,

2016-12-01 13:16 GMT+01:00 Jisheng Zhang <jszhang@...vell.com>:
> On Thu, 1 Dec 2016 20:02:05 +0800 Jisheng Zhang wrote:
>
>> Hi Marcin,
>>
>> On Thu, 1 Dec 2016 12:48:39 +0100 Marcin Wojtas wrote:
>>
>> > Hi Jisheng,
>> >
>> > Which baseline do you use?
>> >
>> > It took me really lot of time to catch why RX broke after rebase from
>> > LKv4.1 to LKv4.4. Between those two, in commit:
>> > 97303480753e ("arm64: Increase the max granular size")
>> > L1_CACHE_BYTES for all ARMv8 platforms was increased to 128B and so
>> > did NET_SKB_PAD.
>> >
>> > And 128 is more than the maximum that can fit into packet offset
>> > [11:8]@0x1400. In such case this correction is needed. Did it answer
>> > your doubts?
>>
>> That's key! Thanks a lot. In my repo, we don't have commit 97303480753e
>> ("arm64: Increase the max granular size")
>>
>> I think it would be great if this information can be added into the commit
>> msg.
>>
>> IIRC, arm64 maintainers considered to let L1_CACHE_BYTES the _minimum_ of
>> cache line sizes of arm64. If that's implemented and merged, then we can
>
> I just searched and found the email.
>
> "We may have to revisit this logic and consider L1_CACHE_BYTES the
> _minimum_ of cache line sizes in arm64 systems supported by the kernel.
> Do you have any benchmarks on Cavium boards that would show significant
> degradation with 64-byte L1_CACHE_BYTES vs 128?"
>
> https://patchwork.kernel.org/patch/8634481/
>
>

Thank you for the information. I debugged it before the discussion. In
future we would be able to revert it, however afair packet offset may
be needed by A3700 Buffer Management.

Best regards,
Marcin

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