Hi lists !
I measured the latency and the jitter of the RX and TX ethernet paths
on my MPC5200 board.
The RX path is quite good, but the TX path can be slow.
[ 1218.976762] [mpc52xx_fec_start_xmit]Delay >30us for dma_map_single
=> 76364 ns
[ 1219.188405] [mpc52xx_fec_tx_interrupt]Delay >30us for
2010/12/1 Jean-Michel Hautbois :
> Hi lists !
>
> I measured the latency and the jitter of the RX and TX ethernet paths
> on my MPC5200 board.
> The RX path is quite good, but the TX path can be slow.
>
> [ 1218.976762] [mpc52xx_fec_start_xmit]Delay >30us for dma_map_single
> => 76364 ns
> [ 1219.1
On Wed, 2010-12-01 at 09:16 +0100, Jean-Michel Hautbois wrote:
> Hi lists !
>
> I measured the latency and the jitter of the RX and TX ethernet paths
> on my MPC5200 board.
> The RX path is quite good, but the TX path can be slow.
>
> [ 1218.976762] [mpc52xx_fec_start_xmit]Delay >30us for dma_map
> A mb() is usually used if you do a write to device and read from it.
> With out it, the CPU could perform the read before the write, which
> would give you an incorrect result. There's no other way around that.
Possibly the synchronisation functions are doing significantly
more work than is re
2010/12/1 David Laight :
>
>> A mb() is usually used if you do a write to device and read from it.
>> With out it, the CPU could perform the read before the write, which
>> would give you an incorrect result. There's no other way around that.
>
> Possibly the synchronisation functions are doing sig
David Laight wrote:
The in_le32() not only contains the unwanted 'sync', but also
a 'twi' (trap immediate - NFI exactly what this does) and 'isync'.
The 'isync' is particularly horrid and unnecessary (aborts
the instruction queue and refeches the opcode bytes).
I've also wondered why some time
On Wed, 1 Dec 2010 15:09:54 +
David Laight wrote:
> The in_le32() not only contains the unwanted 'sync', but also
> a 'twi' (trap immediate - NFI exactly what this does) and 'isync'.
It turns a data dependency into a flow dependency. It's basically equivalent
to:
lwz rX, ...
cmpwr
