On Fri, 2017-02-03 at 13:20 -0800, Shannon Nelson wrote:
> 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@xxxxxxxxxx>
> >> ---
> >> 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().
>
Transmit completion might happen on another cpu, regardless of ldom.
Therefore you need smp_rmb() here ( like mellanox/mlx4/en_tx.c) , or
even smp_mb() as bnx2x does.
dma_rmb() is never used in this context.
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