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From: Martin Lau <kafai@fb.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "bpf@vger.kernel.org" <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@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next 09/13] bpf: Add BPF_FUNC_jiffies
Date: Mon, 16 Dec 2019 21:17:19 +0000	[thread overview]
Message-ID: <20191216211715.uxzcnj4zc3ba2rly@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <a2d8d888-16e1-243d-92c9-56ba3a3e1b18@gmail.com>

On Mon, Dec 16, 2019 at 11:33:01AM -0800, Eric Dumazet wrote:
> 
> 
> On 12/16/19 11:14 AM, Martin Lau wrote:
> > On Fri, Dec 13, 2019 at 05:59:54PM -0800, Eric Dumazet 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.
> > Thanks for the feedbacks!
> > 
> > I have a few questions that need some helps.
> > 
> > Does it mean tp->tcp_mstamp can be used as the "now" in cubic?
> 
> TCP makes sure to update tp->tcp_mstamp at least once when handling
> a particular packet. We did that to avoid calling possibly expensive
> kernel time service (Some platforms do not have fast TSC) 
> 
> > or tcp_clock_ns() should still be called in cubic, e.g. to replace
> > bictcp_clock() and tcp_jiffies32?
> 
> Yeah, there is this lsndtime and tcp_jiffies32 thing, but maybe
> we can find a way to fetch jiffies32 without having to call a bpf helper ?
Loading a kernel global variable is not yet supported.
Thus, helper is needed but it could be inlined like array_map_gen_lookup().

  reply	other threads:[~2019-12-16 21:17 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
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 [this message]
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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