Re: [PATCH net-next 04/12] ibmvnic: Introduce xmit_more support using batched subCRQ hcalls

[Thomas Falcon <tlfalcon@linux.ibm.com>]

On 11/14/20 5:46 PM, Jakub Kicinski wrote:
> On Thu, 12 Nov 2020 13:09:59 -0600 Thomas Falcon wrote:
>> Include support for the xmit_more feature utilizing the
>> H_SEND_SUB_CRQ_INDIRECT hypervisor call which allows the sending
>> of multiple subordinate Command Response Queue descriptors in one
>> hypervisor call via a DMA-mapped buffer. This update reduces hypervisor
>> calls and thus hypervisor call overhead per TX descriptor.
>>
>> Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
> The common bug with xmit_more is not flushing the already queued
> notifications when there is a drop. Any time you drop a skb you need
> to check it's not an skb that was the end of an xmit_more train and
> if so flush notifications (or just always flush on error).
>
> Looking at the driver e.g. this starting goto:
>
>          if (ibmvnic_xmit_workarounds(skb, netdev)) {
>                  tx_dropped++;
>                  tx_send_failed++;
>                  ret = NETDEV_TX_OK;
>                  goto out;
>          }
>
> Does not seem to hit any flush on its way out AFAICS.

Hi, I included those updates in a later patch to ease review but see now 
that that was a mistake. I will merge those bits back into this patch 
and resubmit.

Thanks!