netdev - Re: [PATCH net-next] net: use bulk free in kfree_skb

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Date:   Sun, 24 Mar 2019 17:54:06 +0100
From:   Felix Fietkau <nbd@....name>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net-next] net: use bulk free in kfree_skb_list

On 2019-03-24 12:31, Jesper Dangaard Brouer wrote:
> On Sun, 24 Mar 2019 07:58:34 +0100
> Felix Fietkau <nbd@....name> wrote:
> 
>> Since we're freeing multiple skbs, we might as well use bulk free to save a
>> few cycles. Use the same conditions for bulk free as in napi_consume_skb.
>> 
>> Signed-off-by: Felix Fietkau <nbd@....name>
> 
> Thanks for working on this, it's been on my todo list for a very long
> time. I just discussed this with Florian at NetDevconf.
No problem. It was showing up on my perf traces while improving
mac80211/mt76 performance, so I decided to deal with it now :)

>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> index 2415d9cb9b89..ec030ab7f1e7 100644
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -666,12 +666,39 @@ EXPORT_SYMBOL(kfree_skb);
>>  
>>  void kfree_skb_list(struct sk_buff *segs)
>>  {
>> -	while (segs) {
>> -		struct sk_buff *next = segs->next;
>> +	struct sk_buff *next = segs;
>> +	void *skbs[16];
>> +	int n_skbs = 0;
>>  
>> -		kfree_skb(segs);
>> -		segs = next;
>> +	while ((segs = next) != NULL) {
>> +		next = segs->next;
>> +
>> +		if (!skb_unref(segs))
>> +			continue;
>> +
>> +		if (segs->fclone != SKB_FCLONE_UNAVAILABLE ||
>> +		    n_skbs >= ARRAY_SIZE(skbs)) {
> 
> You could call kmem_cache_free_bulk() here and reset n_skbs=0.
Sure, good idea. I'll send v2 shortly.

- Felix