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From: Jakub Sitnicki <jakub@cloudflare.com>
To: Martin KaFai Lau <kafai@fb.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	Neal Cardwell <ncardwell@google.com>,
	bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	David Miller <davem@davemloft.net>,
	Kernel Team <kernel-team@fb.com>, Netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next 09/13] bpf: Add BPF_FUNC_jiffies
Date: Tue, 17 Dec 2019 09:26:31 +0100	[thread overview]
Message-ID: <87o8w7fjd4.fsf@cloudflare.com> (raw)
In-Reply-To: <CADVnQy=soQ8KhuUWEQj0n2ge3a43OSgAKS95bmBtp090jqbM_w@mail.gmail.com>

On Sat, Dec 14, 2019 at 08:25 PM CET, Neal Cardwell wrote:
> On Fri, Dec 13, 2019 at 9:00 PM Eric Dumazet <eric.dumazet@gmail.com> 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).

Having bpf_nsecs_to_jiffies() would be also handy for BPF sockops progs
that configure SYN-RTO timeout (BPF_SOCK_OPS_TIMEOUT_INIT).

Right now user-space needs to go look for CONFIG_HZ in /proc/config.gz
or /boot/config-`uname -r`, or derive it from clock resolution [0]

        clock_getres(CLOCK_REALTIME_COARSE, &res);
        jiffy = res.tv_nsec / 1000000;

to pass timeout in jiffies to the BPF prog.

-jkbs

[0] https://www.mail-archive.com/kernelnewbies@nl.linux.org/msg08850.html


  parent reply	other threads:[~2019-12-17  8:26 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-14  0:47 [PATCH bpf-next 00/13] Introduce BPF STRUCT_OPS Martin KaFai Lau
2019-12-14  0:47 ` [PATCH bpf-next 01/13] bpf: Save PTR_TO_BTF_ID register state when spilling to stack Martin KaFai Lau
2019-12-16 19:48   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 02/13] bpf: Avoid storing modifier to info->btf_id Martin KaFai Lau
2019-12-16 21:34   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 03/13] bpf: Add enum support to btf_ctx_access() Martin KaFai Lau
2019-12-16 21:36   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 04/13] bpf: Support bitfield read access in btf_struct_access Martin KaFai Lau
2019-12-16 22:05   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 05/13] bpf: Introduce BPF_PROG_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-17  6:14   ` Yonghong Song
2019-12-18 16:41     ` Martin Lau
2019-12-14  0:47 ` [PATCH bpf-next 06/13] bpf: Introduce BPF_MAP_TYPE_STRUCT_OPS Martin KaFai Lau
2019-12-17  7:48   ` [Potential Spoof] " Yonghong Song
2019-12-20  7:22     ` Martin Lau
2019-12-20 16:52       ` Martin Lau
2019-12-20 18:41         ` Andrii Nakryiko
2019-12-14  0:47 ` [PATCH bpf-next 07/13] bpf: tcp: Support tcp_congestion_ops in bpf Martin KaFai Lau
2019-12-17 17:36   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 08/13] bpf: Add BPF_FUNC_tcp_send_ack helper Martin KaFai Lau
2019-12-17 17:41   ` Yonghong Song
2019-12-14  0:47 ` [PATCH bpf-next 09/13] bpf: Add BPF_FUNC_jiffies Martin KaFai Lau
2019-12-14  1:59   ` Eric Dumazet
2019-12-14 19:25     ` Neal Cardwell
2019-12-16 19:30       ` Martin Lau
2019-12-17  8:26       ` Jakub Sitnicki [this message]
2019-12-17 18:22         ` Martin Lau
2019-12-17 21:04           ` Eric Dumazet
2019-12-18  9:03           ` Jakub Sitnicki
2019-12-16 19:14     ` Martin Lau
2019-12-16 19:33       ` Eric Dumazet
2019-12-16 21:17         ` Martin Lau
2019-12-16 23:08       ` Alexei Starovoitov
2019-12-17  0:34         ` Eric Dumazet
2019-12-14  0:48 ` [PATCH bpf-next 10/13] bpf: Synch uapi bpf.h to tools/ Martin KaFai Lau
2019-12-14  0:48 ` [PATCH bpf-next 11/13] bpf: libbpf: Add STRUCT_OPS support Martin KaFai Lau
2019-12-18  3:07   ` Andrii Nakryiko
2019-12-18  7:03     ` Martin Lau
2019-12-18  7:20       ` Martin Lau
2019-12-18 16:36         ` Andrii Nakryiko
2019-12-18 16:34       ` Andrii Nakryiko
2019-12-18 17:33         ` Martin Lau
2019-12-18 18:14           ` Andrii Nakryiko
2019-12-18 20:19             ` Martin Lau
2019-12-19  8:53             ` Toke Høiland-Jørgensen
2019-12-19 20:49               ` Andrii Nakryiko
2019-12-20 10:16                 ` Toke Høiland-Jørgensen
2019-12-20 17:34                   ` Andrii Nakryiko
2019-12-14  0:48 ` [PATCH bpf-next 12/13] bpf: Add bpf_dctcp example Martin KaFai Lau
2019-12-14  0:48 ` [PATCH bpf-next 13/13] bpf: Add bpf_cubic example Martin KaFai Lau
2019-12-14  2:26 ` [PATCH bpf-next 00/13] Introduce BPF STRUCT_OPS Eric Dumazet

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