Re: [PATCH net-next v2 5/9] xsk: add xsk_alloc_batch_skb() to build skbs in batch

On Thu, Aug 28, 2025 at 11:29 PM Alexander Lobakin
[off-list ref] wrote:

From: Jason Xing <redacted>
Date: Thu, 28 Aug 2025 08:38:42 +0800

quoted

On Wed, Aug 27, 2025 at 10:33 PM Alexander Lobakin
[off-list ref] wrote:

quoted

From: Jason Xing <redacted>
Date: Mon, 25 Aug 2025 21:53:38 +0800

quoted

From: Jason Xing <kernelxing@tencent.com>

Support allocating and building skbs in batch.

[...]

quoted

+     base_len = max(NET_SKB_PAD, L1_CACHE_ALIGN(dev->needed_headroom));
+     if (!(dev->priv_flags & IFF_TX_SKB_NO_LINEAR))
+             base_len += dev->needed_tailroom;
+
+     if (xs->skb_count >= nb_pkts)
+             goto build;
+
+     if (xs->skb) {
+             i = 1;
+             xs->skb_count++;
+     }
+
+     xs->skb_count += kmem_cache_alloc_bulk(net_hotdata.skbuff_cache,
+                                            gfp_mask, nb_pkts - xs->skb_count,
+                                            (void **)&skbs[xs->skb_count]);

Have you tried napi_skb_cache_get_bulk()? Depending on the workload, it
may give better perf numbers.

Sure, my initial try is using this interface. But later I want to see
a standalone cache belonging to xsk. The whole xsk_alloc_batch_skb
function I added is quite similar to napi_skb_cache_get_bulk(), to
some extent.

And if using napi_xxx(), we need a lock to avoid the race between this
context and softirq context on the same core.

Are you saying this particular function is not run in the softirq

No, it runs in process context. Please see this chain:
sendto->__xsk_generic_xmit-> (allocating skbs function handling).

Thanks,
Jason

context? I thought all Tx is done in BH.
If it's not BH, then ignore my suggestion -- napi_skb_cache_get_bulk()
requires BH, that's true.

quoted

Thanks,
Jason

Thanks,
Olek