On 12/13/19 4:47 PM, Martin KaFai Lau wrote:
> This patch adds a helper to handle jiffies. Some of the
> tcp_sock's timing is stored in jiffies. Although things
> could be deduced by CONFIG_HZ, having an easy way to get
> jiffies will make the later bpf-tcp-cc implementation easier.
>
...
> +
> +BPF_CALL_2(bpf_jiffies, u64, in, u64, flags)
> +{
> + if (!flags)
> + return get_jiffies_64();
> +
> + if (flags & BPF_F_NS_TO_JIFFIES) {
> + return nsecs_to_jiffies(in);
> + } else if (flags & BPF_F_JIFFIES_TO_NS) {
> + if (!in)
> + in = get_jiffies_64();
> + return jiffies_to_nsecs(in);
> + }
> +
> + return 0;
> +}
This looks a bit convoluted :)
Note that we could possibly change net/ipv4/tcp_cubic.c to no longer use jiffies at all.
We have in tp->tcp_mstamp an accurate timestamp (in usec) that can be converted to ms.
Have you thought of finding a way to not duplicate the code for cubic and dctcp, maybe
by including a template ?
Maintaining two copies means that future changes need more maintenance work.
