netdev - Re: [PATCH net-next 1/6] s390/ctcm: Avoid temporary allocation of struct th_header and th

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Message-ID: <20201201170208.67ba8ac7@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Tue, 1 Dec 2020 17:02:08 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Julian Wiedmann <jwi@...ux.ibm.com>
Cc:     David Miller <davem@...emloft.net>,
        linux-netdev <netdev@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH net-next 1/6] s390/ctcm: Avoid temporary allocation of
 struct th_header and th_sweep.

On Mon, 30 Nov 2020 11:09:45 +0100 Julian Wiedmann wrote:
> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> The size of struct th_header is 8 byte and the size of struct th_sweep
> is 16 byte. The memory for is allocated, initialized, used and
> deallocated a few lines later.
> 
> It is more efficient to avoid the allocation/free dance and assign the
> values directly to skb's data part instead of using memcpy() for it.
> 
> Avoid an allocation of struct th_sweep/th_header and use the resulting
> skb pointer instead.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> [jwi: use skb_put_zero(), instead of skb_put() + memset to 0]
> Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>

Stuff like that is usually done when skb data cannot be assumed to be
aligned. I don't see where the skbs are allocated here, so fingers
crossed :)