[Intel-wired-lan] [PATCH bpf-next 4/4] ixgbe, xsk: use XSK_NAPI_WEIGHT as NAPI poll budget
Björn Töpel
bjorn.topel at intel.com
Tue Sep 8 11:49:54 UTC 2020
On 2020-09-08 11:45, Eric Dumazet wrote:
>
>
> On 9/7/20 5:02 PM, Björn Töpel wrote:
>> From: Björn Töpel <bjorn.topel at intel.com>
>>
>> Start using XSK_NAPI_WEIGHT as NAPI poll budget for the AF_XDP Rx
>> zero-copy path.
>>
>> Signed-off-by: Björn Töpel <bjorn.topel at intel.com>
>> ---
>> drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
>> index 3771857cf887..f32c1ba0d237 100644
>> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
>> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
>> @@ -239,7 +239,7 @@ int ixgbe_clean_rx_irq_zc(struct ixgbe_q_vector *q_vector,
>> bool failure = false;
>> struct sk_buff *skb;
>>
>> - while (likely(total_rx_packets < budget)) {
>> + while (likely(total_rx_packets < XSK_NAPI_WEIGHT)) {
>> union ixgbe_adv_rx_desc *rx_desc;
>> struct ixgbe_rx_buffer *bi;
>> unsigned int size
>
> This is a violation of NAPI API. IXGBE is already diverging a bit from best practices.
>
Thanks for having a look, Eric! By diverging from best practices, do
you mean that multiple queues share one NAPI context, and the budget
is split over the queues (say, 4 queues, 64/4 per queue), or that Tx
simply ignores the budget? Or both?
> There are reasons we want to control the budget from callers,
> if you want bigger budget just increase it instead of using your own ?
>
> I would rather use a generic patch.
>
Hmm, so a configurable NAPI budget for, say, the AF_XDP enabled
queues/NAPIs? Am I reading that correct? (Note that this is *only* for
the AF_XDP enabled queues.)
I'll try to rework this to something more palatable.
Thanks,
Björn
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 7bd4fcdd0738a718d8b0f7134523cd87e4dcdb7b..33bcbdb6fef488983438c6584e3cbb0a44febb1a 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2311,11 +2311,14 @@ static inline void *netdev_priv(const struct net_device *dev)
> */
> #define SET_NETDEV_DEVTYPE(net, devtype) ((net)->dev.type = (devtype))
>
> -/* Default NAPI poll() weight
> - * Device drivers are strongly advised to not use bigger value
> - */
> +/* Default NAPI poll() weight. Highly recommended. */
> #define NAPI_POLL_WEIGHT 64
>
> +/* Device drivers are strongly advised to not use bigger value,
> + * as this might cause latencies in stress conditions.
> + */
> +#define NAPI_POLL_WEIGHT_MAX 256
> +
> /**
> * netif_napi_add - initialize a NAPI context
> * @dev: network device
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4086d335978c1bf62bd3965bd2ea96a4ac06b13d..496713fb6075bd8e5e22725e7c817172858e1dd7 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6608,7 +6608,7 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
> INIT_LIST_HEAD(&napi->rx_list);
> napi->rx_count = 0;
> napi->poll = poll;
> - if (weight > NAPI_POLL_WEIGHT)
> + if (weight > NAPI_POLL_WEIGHT_MAX)
> netdev_err_once(dev, "%s() called with weight %d\n", __func__,
> weight);
> napi->weight = weight;
>
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