Re: [RFC PATCH bpf-next v4 2/2] net: Add additional bit to support clockid_t timestamp type

From: Abhishek Chauhan (ABC)
Date: Thu Apr 18 2024 - 16:11:28 EST



On 4/18/2024 12:06 PM, 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@xxxxxxxxx/
>> Signed-off-by: Abhishek Chauhan <quic_abchauha@xxxxxxxxxxx>
>>
>> /**
>> - * tstamp_type:1 can take 2 values each
>> + * tstamp_type:2 can take 4 values each
>> * represented by time base in skb
>> * 0x0 => real timestamp_type
>> * 0x1 => mono timestamp_type
>> + * 0x2 => tai timestamp_type
>> + * 0x3 => undefined timestamp_type
>
> Same point as previous patch about comment that repeats name.
>
Will take care, Noted!
>> @@ -833,7 +836,8 @@ enum skb_tstamp_type {
>> * @tstamp_type: When set, skb->tstamp has the
>> * delivery_time in mono clock base (i.e. EDT). Otherwise, the
>> * skb->tstamp has the (rcv) timestamp at ingress and
>> - * delivery_time at egress.
>> + * delivery_time at egress or skb->tstamp defined by skb->sk->sk_clockid
>> + * coming from userspace
>
> I would simplify the comment: clock base of skb->tstamp.
> Already in the first patch.
>
Will take care, Noted!
>> * @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.
>> @@ -961,7 +965,7 @@ struct sk_buff {
>> /* private: */
>> __u8 __mono_tc_offset[0];
>> /* public: */
>> - __u8 tstamp_type:1; /* See SKB_CLOCK_*_MASK */
>> + __u8 tstamp_type:2; /* See skb_tstamp_type enum */
>
> Probably good to call out that according to pahole this fills a hole.
>
I will do that .
>> #ifdef CONFIG_NET_XGRESS
>> __u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
>> __u8 tc_skip_classify:1;
>> @@ -1096,10 +1100,12 @@ struct sk_buff {
>> */
>> #ifdef __BIG_ENDIAN_BITFIELD
>> #define SKB_MONO_DELIVERY_TIME_MASK (1 << 7)
>> -#define TC_AT_INGRESS_MASK (1 << 6)
>> +#define SKB_TAI_DELIVERY_TIME_MASK (1 << 6)
>
> SKB_TSTAMP_TYPE_BIT2_MASK?
>
I was thinking to keep it as TAI because it will confuse developers. I hope thats okay.
>> +#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_TAI_DELIVERY_TIME_MASK (1 << 1)
>> +#define TC_AT_INGRESS_MASK (1 << 2)
>> #endif
>> #define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset)
>>
>> @@ -4206,6 +4212,11 @@ static inline void skb_set_delivery_time(struct sk_buff *skb, ktime_t kt,
>> case CLOCK_MONOTONIC:
>> skb->tstamp_type = SKB_CLOCK_MONO;
>> break;
>> + case CLOCK_TAI:
>> + skb->tstamp_type = SKB_CLOCK_TAI;
>> + break;
>> + default:
>> + WARN_ONCE(true, "clockid %d not supported", tstamp_type);
>
> and set to 0 and default tstamp_type?
> Actually thinking about it. I feel if its unsupported just fall back to default is the correct thing. I will take care of this.
>> }
>> }
>
>> >
> @@ -9372,10 +9378,16 @@ static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
>> *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
>> SKB_BF_MONO_TC_OFFSET);
>> *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
>> - SKB_MONO_DELIVERY_TIME_MASK, 2);
>> + SKB_MONO_DELIVERY_TIME_MASK | SKB_TAI_DELIVERY_TIME_MASK, 2);
>> + *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
>> + SKB_MONO_DELIVERY_TIME_MASK, 3);
>> + *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
>> + SKB_TAI_DELIVERY_TIME_MASK, 4);
>> *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_UNSPEC);
>> *insn++ = BPF_JMP_A(1);
>> *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_DELIVERY_MONO);
>> + *insn++ = BPF_JMP_A(1);
>> + *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_DELIVERY_TAI);
>>
>> return insn;
>> }
>> @@ -9418,10 +9430,26 @@ static struct bpf_insn *bpf_convert_tstamp_read(const struct bpf_prog *prog,
>> __u8 tmp_reg = BPF_REG_AX;
>>
>> *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg, SKB_BF_MONO_TC_OFFSET);
>> + /*check if all three bits are set*/
>> *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg,
>> - TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK);
>> - *insn++ = BPF_JMP32_IMM(BPF_JNE, tmp_reg,
>> - TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 2);
>> + TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK |
>> + SKB_TAI_DELIVERY_TIME_MASK);
>> + /*if all 3 bits are set jump 3 instructions and clear the register */
>> + *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
>> + TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK |
>> + SKB_TAI_DELIVERY_TIME_MASK, 4);
>> + /*Now check Mono is set with ingress mask if so clear */
>> + *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
>> + TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK, 3);
>> + /*Now Check tai is set with ingress mask if so clear */
>> + *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
>> + TC_AT_INGRESS_MASK | SKB_TAI_DELIVERY_TIME_MASK, 2);
>> + /*Now Check tai and mono are set if so clear */
>> + *insn++ = BPF_JMP32_IMM(BPF_JEQ, tmp_reg,
>> + SKB_MONO_DELIVERY_TIME_MASK |
>> + SKB_TAI_DELIVERY_TIME_MASK, 1);
>
> This looks as if all JEQ result in "if so clear"?
>
> Is the goal to only do something different for the two bits being 0x1,
> can we have a single test with a two-bit mask, rather than four tests?
>
I think Martin wanted to take care of TAI as well. I will wait for his comment here

My Goal was to take care of invalid combos which does not hold valid
1. If all 3 bits are set => invalid combo (Test case written is Insane)
2. If 2 bits are set (tai+mono)(Test case written is Insane) => this cannot happen (because clock base can only be one in skb)
3. If 2 bit are set (ingress + tai/mono) => This is existing logic + tai being added (clear tstamp in ingress)
4. For all other cases go ahead and fill in the tstamp in the dest register.

>