netdev - Re: [PATCH net-next] r8169: improve rx buffer allocation

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Message-Id: <20190122.145225.1783445146286517629.davem@davemloft.net>
Date:   Tue, 22 Jan 2019 14:52:25 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     hkallweit1@...il.com
Cc:     nic_swsd@...ltek.com, netdev@...r.kernel.org, edumazet@...gle.com
Subject: Re: [PATCH net-next] r8169: improve rx buffer allocation

From: Heiner Kallweit <hkallweit1@...il.com>
Date: Sun, 20 Jan 2019 11:12:01 +0100

> 8 years ago, as part of 6f0333b8fde4 ("r8169: use 50% less ram for RX
> ring"), the alignment requirement for rx buffers was silently changed
> from 8 bytes to 16 bytes. I found nothing explaining this, also the
> chip specs I have only mention an 8 byte requirement.
> AFAICS kmalloc_node() guarantees allocated memory to be at least
> "long long" aligned, what is 8 bytes on a 32 bit machine.
> So we can take this memory as-is and avoid some overhead by changing
> the alignment requirement back to 8 bytes.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>

Applied.

It might have been for cache line alignment or something silly like
that.  But totally undocumented.