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Message-ID: <6b6bd108-817c-4a58-8b69-6c2dde436575@quicinc.com>
Date: Thu, 18 Apr 2024 17:30:42 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
Willem de Bruijn
<willemdebruijn.kernel@...il.com>
CC: "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>,
Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
<kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v4 2/2] net: Add additional bit to support
clockid_t timestamp type
On 4/18/2024 2:57 PM, Martin KaFai Lau wrote:
> On 4/18/24 1:10 PM, Abhishek Chauhan (ABC) wrote:
>>>> #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?
>
> nit. Shorten it to just SKB_TSTAMP_TYPE_MASK?
>
Okay i will do the same. Noted!
> #ifdef __BIG_ENDIAN_BITFIELD
> #define SKB_TSTAMP_TYPE_MASK (3 << 6)
> #define SKB_TSTAMP_TYPE_RSH (6) /* more on this later */
> #else
> #define SKB_TSTAMP_TYPE_MASK (3)
> #endif
>
>>>
>> I was thinking to keep it as TAI because it will confuse developers. I hope thats okay.
>
> I think it is not very useful to distinguish each bit since it is an enum value now. It becomes more like the "pkt_type:3" and its PKT_TYPE_MAX.
>I see what you are saying.
>>>> +#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);
>
> With SKB_TSTAMP_TYPE_MASK defined like above, this could be simplified like this (untested):
>
Let me think this through and raise it as part of the next rfc patch.
> static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
> struct bpf_insn *insn)
> {
> __u8 value_reg = si->dst_reg;
> __u8 skb_reg = si->src_reg;
>
> BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
> *insn++ = BPF_LDX_MEM(BPF_B, value_reg, skb_reg, SKB_BF_MONO_TC_OFFSET);
> *insn++ = BPF_ALU32_IMM(BPF_AND, value_reg, SKB_TSTAMP_TYPE_MASK);
> #ifdef __BIG_ENDIAN_BITFIELD
> *insn++ = BPF_ALU32_IMM(BPF_RSH, value_reg, SKB_TSTAMP_TYPE_RSH);
> #else
> BUILD_BUG_ON(!(SKB_TSTAMP_TYPE_MASK & 0x1));
> #endif
>
> return insn;
> }
>
>>>> 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);
>
> Same as the bpf_convert_tstamp_type_read, this could be simplified with SKB_TSTAMP_TYPE_MASK.
>
>>>
>>> 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.
>
> If it is to ensure no new type is added without adding BPF_SKB_TSTAMP_DELIVERY_XYZ, I would simplify this runtime bpf insns here and use a BUILD_BUG_ON to catch it at compile time. Something like,
>
> enum skb_tstamp_type {
> SKB_CLOCK_REAL, /* Time base is skb is REALTIME */
> SKB_CLOCK_MONO, /* Time base is skb is MONOTONIC */
> SKB_CLOCK_TAI, /* Time base in skb is TAI */
> __SKB_CLOCK_MAX = SKB_CLOCK_TAI,
> };
>
> /* Same one used in the bpf_convert_tstamp_type_read() above */
> BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
>
> Another thing is, the UDP test in test_tc_dtime.c probably needs to be adjusted, the userspace is using the CLOCK_TAI in SO_TXTIME and it is getting forwarded now.
Noted ! Let me check and evalute this as well.
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