Messages in this thread | | | Date | Wed, 10 Apr 2024 16:25:57 -0700 | Subject | Re: [RFC PATCH bpf-next v1 3/3] net: Add additional bit to support userspace timestamp type | From | Martin KaFai Lau <> |
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On 4/10/24 1:25 PM, Abhishek Chauhan (ABC) wrote: >>> @@ -830,6 +833,9 @@ enum skb_tstamp_type { >>> * 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 in mono clock base (i.e., EDT) or a clock base chosen >>> + * by SO_TXTIME. If zero, skb->tstamp has the (rcv) timestamp at >>> + * ingress. >>> * @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 +966,7 @@ struct sk_buff { >>> /* private: */ >>> __u8 __mono_tc_offset[0]; >>> /* public: */ >>> - __u8 tstamp_type:1; /* See SKB_MONO_DELIVERY_TIME_MASK */ >>> + __u8 tstamp_type:2; /* See SKB_MONO_DELIVERY_TIME_MASK */ >>> #ifdef CONFIG_NET_XGRESS >>> __u8 tc_at_ingress:1; /* See TC_AT_INGRESS_MASK */
The above "tstamp_type:2" change shifted the tc_at_ingress bit. TC_AT_INGRESS_MASK needs to be adjusted.
>>> __u8 tc_skip_classify:1; >> >> With pahole, does this have an effect on sk_buff layout? >> > I think it does and it also impacts BPF testing. Hence in my cover letter i have mentioned that these > changes will impact BPF. My level of expertise is very limited to BPF hence the reason for RFC. > That being said i am actually trying to understand/learn BPF instructions to know things better. > I think we need to also change the offset SKB_MONO_DELIVERY_TIME_MASK and TC_AT_INGRESS_MASK > > > #ifdef __BIG_ENDIAN_BITFIELD > #define SKB_MONO_DELIVERY_TIME_MASK (1 << 7) //Suspecting changes here too > #define TC_AT_INGRESS_MASK (1 << 6) // and here > #else > #define SKB_MONO_DELIVERY_TIME_MASK (1 << 0) > #define TC_AT_INGRESS_MASK (1 << 1) (this might have to change to 1<<2 )
This should be (1 << 2) now. Similar adjustment for the big endian.
> #endif > #define SKB_BF_MONO_TC_OFFSET offsetof(struct sk_buff, __mono_tc_offset) > > Also i suspect i change in /selftests/bpf/prog_tests/ctx_rewrite.c
ctx_rewrite.c tests the bpf ctx rewrite code. In this particular case, it tests the bpf_convert_tstamp_read() and bpf_convert_tstamp_write() generate the correct bpf instructions. e.g. "w11 &= 3;" is testing the following in bpf_convert_tstamp_read(): *insn++ = BPF_ALU32_IMM(BPF_AND, tmp_reg, TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK);
The existing "TC_AT_INGRESS_MASK | SKB_MONO_DELIVERY_TIME_MASK" is 0x3 and it should become 0x5 if my hand counts correctly.
The patch set cannot be applied to the bpf-next: https://patchwork.kernel.org/project/netdevbpf/patch/20240409210547.3815806-4-quic_abchauha@quicinc.com/ , so bpf CI cannot run to reproduce the issue.
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