Re: [dpdk-dev] [PATCH v2] net/af_packet: fix ignoring full ring on tx

On Tue, 26 Oct 2021 at 17:41, Ferruh Yigit [off-list ref] wrote:

Hi Tudor,

I have used testpmd, 'txonly' forwarding. Tx recovers after interface up,
but by adding some debug logs I can see 'poll()' returns with POLLOUT even
there is no space in the buffer.

According the logic in the PMD, when 'poll()' returns success, it expects
to have some space in the Tx buffer.

So I agree to add the check.

Only have a question on the POLLERR, should we separate the POLLERR check
to cover ifdown case, what do you think about following logic:

if (!TP_STATUS_AVAILABLE) {
     if (poll() < 0)
         break;
     if (pfd.revents & POLLERR)
         break;
}

if (!TP_STATUS_AVAILABLE)
     break;

Hi Ferruh,

Thanks for the suggestion.
I was thinking of adding this check, and intuitively, it seems correct. I
tried to do some further testing.

I tested with the POLLERR check, and I don't see the issue anymore.
However, if I remove the second if (!TP_STATUS_AVAILABLE), I seem to get
bursts of 2048 packets followed by periods of not sending anything when
toggling the interface link state.
Without the second if(!TP_STATUS_AVAILABLE) statement, the issue seems to
reproduce, regardless if I add the check for POLLERR or not.

RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=606208 TxP=2048
RxB=0 RxP=0 TxB=0 TxP=0
RxB=0 RxP=0 TxB=0 TxP=0

I will send an updated version of the patch.

Thanks,
Tudor