netdev - Re: [PATCH net-next 6/7] net: dsa: remove useless copy of tagger xmit

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Message-ID: <87zidu2vut.fsf@weeman.i-did-not-set--mail-host-address--so-tickle-me>
Date:   Tue, 30 May 2017 11:43:54 -0400
From:   Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...oirfairelinux.com,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH net-next 6/7] net: dsa: remove useless copy of tagger xmit

Hi Andrew,

Andrew Lunn <andrew@...n.ch> writes:

>>  	/* Transmit function may have to reallocate the original SKB */
>> -	nskb = p->xmit(skb, dev);
>> +	nskb = p->dp->ds->dst->tag_ops->xmit(skb, dev);
>
> This is also the hot path for DSA transmit. Do we really want to do 4
> extra pointer dereferences a million times per second, compared to one
> copy during setup?

Yep I get the idea. It felt weird to copy structure members like this
and not at least reusing the dsa_device_ops structure.

Thanks,

        Vivien