netdev - Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid

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Message-ID: <76cc402a-9513-433f-b40b-f3ae93c6d65f@quicinc.com>
Date: Thu, 25 Apr 2024 12:12:52 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Andrew Halaney <ahalaney@...hat.com>,
        "Martin
 KaFai Lau" <martin.lau@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>
CC: <kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support
 clockid_t timestamp type



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@...cinc.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. 
> 
>