netdev - Re: [PATCH net-next 01/10] net: stmmac: Let descriptor code set skbuff address

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Date:   Thu, 10 May 2018 15:06:13 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     Jose.Abreu@...opsys.com
Cc:     netdev@...r.kernel.org, Joao.Pinto@...opsys.com,
        Vitor.Soares@...opsys.com, peppe.cavallaro@...com,
        alexandre.torgue@...com
Subject: Re: [PATCH net-next 01/10] net: stmmac: Let descriptor code set
 skbuff address

From: Jose Abreu <Jose.Abreu@...opsys.com>
Date: Tue,  8 May 2018 15:45:24 +0100

> Stop using if conditions depending on the GMAC version for setting the
> the descriptor skbuff address and use instead a helper implemented in
> the descriptor files.
> 
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>

With Spectre mitigations, indirect calls are extremely expensive.  Much
more expensive than conditional checks.

And since this is the descriptor setup in the fast paths of the driver,
I advise that you keep these conditionals.