Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid_t timestamp type

Abhishek Chauhan (ABC)
2024-04-25T19:13:23Z

On 4/25/2024 7:42 AM, Willem de Bruijn wrote:
> Abhishek Chauhan wrote:
>> tstamp_type is now set based on actual clockid_t compressed
>> into 2 bits.
>>
>> To make the design scalable for future needs this commit bring in
>> the change to extend the tstamp_type:1 to tstamp_type:2 to support
>> other clockid_t timestamp.
>>
>> We now support CLOCK_TAI as part of tstamp_type as part of this
>> commit with exisiting support CLOCK_MONOTONIC and CLOCK_REALTIME.
>>
>> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
>> Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
>> ---
>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index e464d0ebc9c1..3ad0de07d261 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -711,6 +711,8 @@ typedef unsigned char *sk_buff_data_t;
>> enum skb_tstamp_type {
>> SKB_CLOCK_REALTIME,
>> SKB_CLOCK_MONOTONIC,
>> + SKB_CLOCK_TAI,
>> + __SKB_CLOCK_MAX = SKB_CLOCK_TAI,
>> };
>>
>> /**
>> @@ -831,8 +833,8 @@ enum skb_tstamp_type {
>> * @decrypted: Decrypted SKB
>> * @slow_gro: state present at GRO time, slower prepare step required
>> * @tstamp_type: When set, skb->tstamp has the
>> - * delivery_time in mono clock base Otherwise, the
>> - * timestamp is considered real clock base.
>> + * delivery_time in mono clock base or clock base of skb->tstamp.
>
> drop "in mono clock base or "
>
Noted
>> + * Otherwise, the timestamp is considered real clock base
>
Noted
> drop this: whenever in realtime clock base, tstamp_type is zero, so
> the above shorter statement always holds.
>
>> * @napi_id: id of the NAPI struct this skb came from
>> * @sender_cpu: (aka @napi_id) source CPU in XPS
>> * @alloc_cpu: CPU which did the skb allocation.
>> @@ -960,7 +962,7 @@ struct sk_buff {
>> /* private: */
>> __u8 __mono_tc_offset[0];
>> /* public: */
>> - __u8 tstamp_type:1; /* See skb_tstamp_type */
>> + __u8 tstamp_type:2; /* See skb_tstamp_type */
>> #ifdef CONFIG_NET_XGRESS
>> __u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
>> __u8 tc_skip_classify:1;
>> @@ -1090,15 +1092,17 @@ struct sk_buff {
>> #endif
>> #define PKT_TYPE_OFFSET offsetof(struct sk_buff, __pkt_type_offset)
>>
>> -/* if you move tc_at_ingress or mono_delivery_time
>> +/* if you move tc_at_ingress or tstamp_type:2
>> * around, you also must adapt these constants.
>> */
>> #ifdef __BIG_ENDIAN_BITFIELD
>> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 7)
>> -#define TC_AT_INGRESS_MASK (1 << 6)
>> +#define SKB_TSTAMP_TYPE_MASK (3 << 6)
>> +#define SKB_TSTAMP_TYPE_RSH (6)
>> +#define TC_AT_INGRESS_RSH (5)
>
> I had to find BPF_RSH to understand this abbreviation.
>
> use SHIFT instead of RSH, as that is so domain specific?
>
Noted! I will use complete words instead of abbreviations
>> +#define TC_AT_INGRESS_MASK (1 << 5)
>> #else
>> -#define SKB_MONO_DELIVERY_TIME_MASK (1 << 0)
>> -#define TC_AT_INGRESS_MASK (1 << 1)
>> +#define SKB_TSTAMP_TYPE_MASK (3)
>> +#define TC_AT_INGRESS_MASK (1 << 2)
>> #endif
>> #define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset)
>>
>
>> - if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO) {
>> + if (skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_MONO ||
>> + skb->tstamp_type == BPF_SKB_TSTAMP_DELIVERY_TAI) {
>
> Peculiar indentation?
>
Let me check why the indentation here is messed up. Ideally i run checkpatch(shows 0 errors or warnings)
and also check before raising a patch. Internally it looks good but on the patch it shows differently.

> Just FYI that I'm not the best person to review the BPF part.
> Thankfully Martin is helping you with that.
>
I will wait for comments from Martin as well.
>
>