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From: "Björn Töpel" <bjorn.topel@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Netdev <netdev@vger.kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Björn Töpel" <bjorn.topel@intel.com>, bpf <bpf@vger.kernel.org>,
	"Magnus Karlsson" <magnus.karlsson@gmail.com>,
	"Karlsson, Magnus" <magnus.karlsson@intel.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Edward Cree" <ecree@solarflare.com>
Subject: Re: [RFC PATCH bpf-next 2/4] bpf: introduce BPF dispatcher
Date: Fri, 15 Nov 2019 08:56:59 +0100	[thread overview]
Message-ID: <CAJ+HfNhKWND35Jnwe=99=8rWt81fhy9pRpXCVRYTu=C=aj13KQ@mail.gmail.com> (raw)
In-Reply-To: <20191115003024.h7eg2kbve23jmzqn@ast-mbp.dhcp.thefacebook.com>

On Fri, 15 Nov 2019 at 01:30, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
[...]
>
> Could you try optimizing emit_mov_imm64() to recognize s32 ?
> iirc there was a single x86 insns that could move and sign extend.
> That should cut down on bytecode size and probably make things a bit faster?
> Another alternative is compare lower 32-bit only, since on x86-64 upper 32
> should be ~0 anyway for bpf prog pointers.

Good ideas, thanks! I'll do the optimization, extend it to >4 entries
(as Toke suggested), and do a non-RFC respin.

> Looking at bookkeeping code, I think I should be able to generalize bpf
> trampoline a bit and share the code for bpf dispatch.

Ok, good!

> Could you also try aligning jmp target a bit by inserting nops?
> Some x86 cpus are sensitive to jmp target alignment. Even without considering
> JCC bug it could be helpful. Especially since we're talking about XDP/AF_XDP
> here that will be pushing millions of calls through bpf dispatch.
>

Yeah, I need to address the Jcc bug anyway, so that makes sense.

Another thought; I'm using the fentry nop as patch point, so it wont
play nice with other users of fentry atm -- but the plan is to move to
Steve's *_ftrace_direct work at some point, correct?


Björn

  reply	other threads:[~2019-11-15  7:57 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-13 20:47 [RFC PATCH bpf-next 0/4] Introduce xdp_call.h and the BPF dispatcher Björn Töpel
2019-11-13 20:47 ` [RFC PATCH bpf-next 1/4] bpf: teach bpf_arch_text_poke() jumps Björn Töpel
2019-11-13 20:47 ` [RFC PATCH bpf-next 2/4] bpf: introduce BPF dispatcher Björn Töpel
2019-11-13 21:40   ` Edward Cree
2019-11-14  6:29     ` Björn Töpel
2019-11-14 10:18       ` Edward Cree
2019-11-14 11:21         ` Björn Töpel
2019-11-14 13:58           ` Peter Zijlstra
2019-11-14 12:31   ` Toke Høiland-Jørgensen
2019-11-14 13:03     ` Daniel Borkmann
2019-11-14 13:09       ` Toke Høiland-Jørgensen
2019-11-14 13:56       ` Björn Töpel
2019-11-14 14:55         ` Toke Høiland-Jørgensen
2019-11-14 15:03           ` Björn Töpel
2019-11-14 15:12             ` Toke Høiland-Jørgensen
2019-11-15  0:30   ` Alexei Starovoitov
2019-11-15  7:56     ` Björn Töpel [this message]
2019-11-15 21:58       ` Alexei Starovoitov
2019-11-18 10:03         ` Björn Töpel
2019-11-18 19:36   ` Andrii Nakryiko
2019-11-18 20:11     ` Björn Töpel
2019-11-13 20:47 ` [RFC PATCH bpf-next 3/4] xdp: introduce xdp_call Björn Töpel
2019-11-13 20:47 ` [RFC PATCH bpf-next 4/4] i40e: start using xdp_call.h Björn Töpel

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