[PATCH v15 05/20] nvme-tcp: Add DDP offload control path
Sagi Grimberg
sagi at grimberg.me
Wed Sep 13 03:46:45 PDT 2023
On 9/13/23 12:10, Aurelien Aptel wrote:
> Sagi Grimberg <sagi at grimberg.me> writes:
>>> + if (test_bit(NVME_TCP_Q_OFF_DDP, &queue->flags))
>>> + nvme_tcp_unoffload_socket(queue);
>>> +#ifdef CONFIG_ULP_DDP
>>> + if (nvme_tcp_admin_queue(queue) && queue->ctrl->ddp_netdev) {
>>> + /* put back ref from get_netdev_for_sock() */
>>> + dev_put(queue->ctrl->ddp_netdev);
>>> + queue->ctrl->ddp_netdev = NULL;
>>> + }
>>> +#endif
>>
>> Lets avoid spraying these ifdefs in the code.
>> the ddp_netdev struct member can be lifted out of the ifdef I think
>> because its only controller-wide.
>>
>
> Ok, we will remove the ifdefs.
>
>>> +#ifdef CONFIG_ULP_DDP
>>> + /*
>>> + * Admin queue takes a netdev ref here, and puts it
>>> + * when the queue is stopped in __nvme_tcp_stop_queue().
>>> + */
>>> + ctrl->ddp_netdev = get_netdev_for_sock(queue->sock->sk);
>>> + if (ctrl->ddp_netdev) {
>>> + if (nvme_tcp_ddp_query_limits(ctrl)) {
>>> + nvme_tcp_ddp_apply_limits(ctrl);
>>> + } else {
>>> + dev_put(ctrl->ddp_netdev);
>>> + ctrl->ddp_netdev = NULL;
>>> + }
>>> + } else {
>>> + dev_info(nctrl->device, "netdev not found\n");
>>
>> Would prefer to not print offload specific messages in non-offload code
>> paths. at best, dev_dbg.
>
> Sure, we will switch to dev_dbg.
>
>> If the netdev is derived by the sk, why does the interface need a netdev
>> at all? why not just pass sk and derive the netdev from the sk behind
>> the interface?
>>
>> Or is there a case that I'm not seeing here?
>
> If we derive the netdev from the socket, it would be too costly to call
> get_netdev_for_sock() which takes a lock on the data path.
>
> We could store it in the existing sk->ulp_ddp_ctx, assigning it in
> sk_add and accessing it in sk_del/setup/teardown/resync.
> But we would run into the problem of not being sure
> get_netdev_for_sock() returned the same device in query_limits() and
> sk_add() because we did not keep a pointer to it.
>
> We believe it would be more complex to deal with these problems than to
> just keep a reference to the netdev in the nvme-tcp controller.
>
OK, Seems though that the netdev and the limits are bundled together,
meaning that you either get both or none.
Perhaps you should bundle them together:
ctrl->ddp_netdev = nvme_tcp_get_ddp_netdev_with_limits(ctrl);
if (ctrl->ddp_netdev)
nvme_tcp_ddp_apply_ctrl_limits(ctrl);
where:
static struct net_device* nvme_tcp_get_ddp_netdev_with_limits(struct
nvme_tcp_ctrl *ctrl)
{
if (!ddp_offload)
return NULL;
netdev = get_netdev_for_sock(ctrl->queues[0].sock->sk);
if (!netdev)
return NULL;
ret = ulp_ddp_query_limits(netdev, &ctrl->ddp_limits,
ULP_DDP_NVME, ULP_DDP_C_NVME_TCP_BIT,
false /* tls */);
if (ret) {
dev_put(netdev);
return NULL;
}
return netdev;
}
And perhaps its time to introduce nvme_tcp_stop_admin_queue()?
static void nvme_tcp_stop_admin_queue(struct nvme_ctrl *nctrl)
{
struct nvme_tcp_ctrl *ctrl = to_tcp_ctrl(nctrl);
nvme_tcp_stop_queue(nctrl, 0);
dev_put(ctrl->ddp_netdev);
}
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