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Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check for tx enable

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On 2/3/2017 9:56 AM, Eric Dumazet wrote:
> On Fri, 2017-02-03 at 09:42 -0800, Shannon Nelson wrote:
>> In order to allow the underlying LDC and outstanding memory operations
>> to potentially catch up with the driver's Tx requests, add a memory
>> barrier before checking again for available tx descriptors.
>>
>> Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
>> ---
>>  drivers/net/ethernet/sun/sunvnet_common.c |    1 +
>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/sun/sunvnet_common.c b/drivers/net/ethernet/sun/sunvnet_common.c
>> index 5d0d386..98e758e 100644
>> --- a/drivers/net/ethernet/sun/sunvnet_common.c
>> +++ b/drivers/net/ethernet/sun/sunvnet_common.c
>> @@ -1467,6 +1467,7 @@ ldc_start_done:
>>  	dr->prod = (dr->prod + 1) & (VNET_TX_RING_SIZE - 1);
>>  	if (unlikely(vnet_tx_dring_avail(dr) < 1)) {
>>  		netif_tx_stop_queue(txq);
>> +		dma_wmb();
>
> This does not look right.
>
> I believe you need smp_rmb() here.

Well, it probably should be dma_rmb(), since regardless of the number of 
cores we think we have, we're communicating with a peer ldom that has 
its own core(s).  Either way, on sparc they all seem to boil down to the 
same bit of asm, but using the "rmb" part makes more logical sense. 
I'll respin with dma_rmb().

Good catch, thanks,
sln


>
>>  		if (vnet_tx_dring_avail(dr) > VNET_TX_WAKEUP_THRESH(dr))
>>  			netif_tx_wake_queue(txq);
>>  	}
>
>

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[PATCH net-next 5/9] sunvnet: add memory barrier before check for tx enable Shannon Nelson <shannon.nelson@oracle.com> - 2017-02-03 18:50 +0100
  Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check  for tx enable Eric Dumazet <eric.dumazet@gmail.com> - 2017-02-03 19:00 +0100
    Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check for  tx enable Shannon Nelson <shannon.nelson@oracle.com> - 2017-02-03 22:30 +0100
      Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check  for tx enable David Miller <davem@davemloft.net> - 2017-02-03 23:00 +0100
      Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check  for tx enable Eric Dumazet <eric.dumazet@gmail.com> - 2017-02-03 23:20 +0100
        Re: [PATCH net-next 5/9] sunvnet: add memory barrier before check for  tx enable Shannon Nelson <shannon.nelson@oracle.com> - 2017-02-04 23:40 +0100

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