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Message-ID: <3a5c8a23-bc03-e79b-47ef-b67f66452327@huawei.com>
Date: Thu, 17 Sep 2020 14:52:54 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Eric Dumazet <edumazet@...gle.com>,
Saeed Mahameed <saeed@...nel.org>
CC: Saeed Mahameed <saeedm@...dia.com>,
"tanhuazhong@...wei.com" <tanhuazhong@...wei.com>,
"davem@...emloft.net" <davem@...emloft.net>,
"yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
"salil.mehta@...wei.com" <salil.mehta@...wei.com>,
"linuxarm@...wei.com" <linuxarm@...wei.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH net-next 6/6] net: hns3: use napi_consume_skb() when
cleaning tx desc
On 2020/9/16 16:38, Eric Dumazet wrote:
> On Wed, Sep 16, 2020 at 10:33 AM Saeed Mahameed <saeed@...nel.org> wrote:
>>
>> On Tue, 2020-09-15 at 15:04 +0800, Yunsheng Lin wrote:
>>> On 2020/9/15 13:09, Saeed Mahameed wrote:
>>>> On Mon, 2020-09-14 at 20:06 +0800, Huazhong Tan wrote:
>>>>> From: Yunsheng Lin <linyunsheng@...wei.com>
>>>>>
>>>>> Use napi_consume_skb() to batch consuming skb when cleaning
>>>>> tx desc in NAPI polling.
>>>>>
>>>>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>>>>> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
>>>>> ---
>>>>> drivers/net/ethernet/hisilicon/hns3/hns3_enet.c | 27
>>>>> +++++++++++-
>>>>> ----------
>>>>> drivers/net/ethernet/hisilicon/hns3/hns3_enet.h | 2 +-
>>>>> drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c | 4 ++--
>>>>> 3 files changed, 17 insertions(+), 16 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>>>>> b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>>>>> index 4a49a76..feeaf75 100644
>>>>> --- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>>>>> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
>>>>> @@ -2333,10 +2333,10 @@ static int hns3_alloc_buffer(struct
>>>>> hns3_enet_ring *ring,
>>>>> }
>>>>>
>>>>> static void hns3_free_buffer(struct hns3_enet_ring *ring,
>>>>> - struct hns3_desc_cb *cb)
>>>>> + struct hns3_desc_cb *cb, int budget)
>>>>> {
>>>>> if (cb->type == DESC_TYPE_SKB)
>>>>> - dev_kfree_skb_any((struct sk_buff *)cb->priv);
>>>>> + napi_consume_skb(cb->priv, budget);
>>>>
>>>> This code can be reached from hns3_lb_clear_tx_ring() below which
>>>> is
>>>> your loopback test and called with non-zero budget, I am not sure
>>>> you
>>>> are allowed to call napi_consume_skb() with non-zero budget outside
>>>> napi context, perhaps the cb->type for loopback test is different
>>>> in lb
>>>> test case ? Idk.. , please double check other code paths.
>>>
>>> Yes, loopback test may call napi_consume_skb() with non-zero budget
>>> outside
>>> napi context. Thanks for pointing out this case.
>>>
>>> How about add the below WARN_ONCE() in napi_consume_skb() to catch
>>> this
>>> kind of error?
>>>
>>> WARN_ONCE(!in_serving_softirq(), "napi_consume_skb() is called with
>>> non-zero budget outside napi context");
>>>
>>
>> Cc: Eric
>>
>> I don't know, need to check performance impact.
>> And in_serving_softirq() doesn't necessarily mean in napi
>> but looking at _kfree_skb_defer(), i think it shouldn't care if napi or
>> not as long as it runs in soft irq it will push the skb to that
>> particular cpu napi_alloc_cache, which should be fine.
Yes, we only need to ensure _kfree_skb_defer() runs with automic context.
And it seems NAPI polling can be in thread context with BH disabled in below
patch, so in_softirq() checking should be more future-proof?
* in_softirq() - We have BH disabled, or are processing softirqs
net: add support for threaded NAPI polling
https://www.mail-archive.com/netdev@vger.kernel.org/msg348491.html
>>
>> Maybe instead of the WARN_ONCE just remove the budget condition and
>> replace it with
>>
>> if (!in_serving_softirq())
>> dev_consume_skb_any(skb);
Yes, that is good idea, _kfree_skb_defer() is only called in softirq or
BH disabled context, dev_consume_skb_any(skb) is called in other context,
so driver author do not need to worry about the calling context of the
napi_consume_skb().
>>
>
> I think we need to keep costs small.
>
> So lets add a CONFIG_DEBUG_NET option so that developers can add
> various DEBUG_NET() clauses.
Do you means something like below:
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 157e024..61a6a62 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5104,6 +5104,15 @@ do { \
})
#endif
+#if defined(CONFIG_DEBUG_NET)
+#define DEBUG_NET_WARN(condition, format...) \
+ do { \
+ WARN(condition, ##__VA_ARGS__);
+ } while (0)
+#else
+#define DEBUG_NET_WARN(condition, format...)
+#endif
+
/*
* The list of packet types we will receive (as opposed to discard)
* and the routines to invoke.
diff --git a/net/Kconfig b/net/Kconfig
index 3831206..f59ea4b 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -473,3 +473,9 @@ config HAVE_CBPF_JIT
# Extended BPF JIT (eBPF)
config HAVE_EBPF_JIT
bool
+
+config DEBUG_NET
+ bool
+ depends on DEBUG_KERNEL
+ help
+ Say Y here to add some extra checks and diagnostics to networking.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bfd7483..10547db 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -904,6 +904,9 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
return;
}
+ DEBUG_NET_WARN(!in_serving_softirq(),
+ "napi_consume_skb() is called with non-zero budget outside softirq context");
+
if (!skb_unref(skb))
return;
> .
>
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