On Fri, Dec 13, 2019 at 9:00 PM Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>
>
>
> 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.
If the jiffies functionality stays, how about 3 simple functions that
correspond to the underlying C functions, perhaps something like:
bpf_nsecs_to_jiffies(nsecs)
bpf_jiffies_to_nsecs(jiffies)
bpf_get_jiffies_64()
Separate functions might be easier to read/maintain (and may even be
faster, given the corresponding reduction in branches).
neal
