netdev - Re: Net: ucc_geth ethernet driver optimization space

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Date:	Wed, 27 May 2009 08:49:09 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	"Liu Dave-R63238" <DaveLiu@...escale.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	linuxppc-dev-bounces+joakim.tjernlund=transmode.se@...abs.org,
	netdev@...r.kernel.org
Subject: Re: Net: ucc_geth ethernet driver optimization space



linuxppc-dev-bounces+joakim.tjernlund=transmode.se@...abs.org wrote on 27/05/2009 07:08:07:
>
> Guys,
>
> The ucc_geth ethernet driver have dozens of strong sync read/write
> operation, such as in_be32/16/8, out_be32/16/8.
>
> all of them is sync read/write, it is very expensive for performance.
>
> For the critical patch, we can remove some unnecessary in_be(x),
> out_be(x) with normal memory operation, and keep some necessary
> memory barrier.
>
> eg: BD access in the interrupt handler and start_xmit.
>
> The BD operation only need the memory barrier between length/buffer
> and status.
>
> struct buffer descriptor {
>    u16 status;
>    u16 length;
>    u32 buffer;
> } __attribute__ ((packed));
>
> struct buffer descriptor *BD;
>
> BD->length = xxxx;
> BD->buffer = yyyy;
> wmb();
> BD->status = zzzz;
>
> For powerpc, eieio is enough for 60x, mbar 1 is enough for e500.
> Of couse, also need the memory clobber to avoid the compiler
> reorder between them.
>
> Thanks, Dave

Yes, pretty please :)

You might want to combine status and length into one U32 though:
BD->buffer = yyyy;
wmb();
BD->stat_len = zzzz << 16 | xxxx;

  Jocke

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