netdev - Re: [PATCH v2 bpf-next 0/7] bpf_prog

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Message-ID: <CAEf4BzZy3TrBoEuGZqzT99YEwwNjTbhp5GY0BW0gXxGzxf8jFQ@mail.gmail.com>
Date:   Fri, 17 Dec 2021 09:16:49 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        Peter Ziljstra <peterz@...radead.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v2 bpf-next 0/7] bpf_prog_pack allocator

On Fri, Dec 17, 2021 at 9:13 AM Song Liu <songliubraving@...com> wrote:
>
>
>
> > On Dec 17, 2021, at 8:43 AM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> >
> > On Fri, Dec 17, 2021 at 8:42 AM Andrii Nakryiko
> > <andrii.nakryiko@...il.com> wrote:
> >>
> >> On Thu, Dec 16, 2021 at 5:53 PM Song Liu <songliubraving@...com> wrote:
> >>>
> >>>
> >>>
> >>>> On Dec 16, 2021, at 12:06 PM, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> >>>>
> >>>> On Tue, Dec 14, 2021 at 10:01 PM Song Liu <song@...nel.org> wrote:
> >>>>>
> >>>>> Changes v1 => v2:
> >>>>> 1. Use text_poke instead of writing through linear mapping. (Peter)
> >>>>> 2. Avoid making changes to non-x86_64 code.
> >>>>>
> >>>>> Most BPF programs are small, but they consume a page each. For systems
> >>>>> with busy traffic and many BPF programs, this could also add significant
> >>>>> pressure to instruction TLB.
> >>>>>
> >>>>> This set tries to solve this problem with customized allocator that pack
> >>>>> multiple programs into a huge page.
> >>>>>
> >>>>> Patches 1-5 prepare the work. Patch 6 contains key logic of the allocator.
> >>>>> Patch 7 uses this allocator in x86_64 jit compiler.
> >>>>>
> >>>>
> >>>> There are test failures, please see [0]. But I was also wondering if
> >>>> there could be an explicit selftest added to validate that all this
> >>>> huge page machinery is actually activated and working as expected?
> >>>
> >>> We can enable some debug option that dumps the page table. Then from the
> >>> page table, we can confirm the programs are running on a huge page. This
> >>> only works on x86_64 though. WDYT?
> >>>
> >>
> >> I don't know what exactly is involved, so it's hard to say. Ideally
> >> whatever we do doesn't complicate our CI setup. Can we use BPF tracing
> >> magic to check this from inside the kernel somehow?
> >>
> >
> > But I don't feel strongly about this, if it's hard to detect, it's
> > fine to not have a specific test (especially that it's very
> > architecture-specific)
>
> It will be more or less architecture-specific, as we need somehow walk
> the page table (with debug option or with BPF iterator). I will try
> something.

If BPF iterator approach works, that would be great!

>
> Thanks,
> Song
>
>
> >
> >>> Thanks,
> >>> Song
> >>>
> >>>
> >>>>
> >>>> [0] https://github.com/kernel-patches/bpf/runs/4530372387?check_suite_focus=true
> >>>>
> >>>>> Song Liu (7):
> >>>>> x86/Kconfig: select HAVE_ARCH_HUGE_VMALLOC with HAVE_ARCH_HUGE_VMAP
> >>>>> bpf: use bytes instead of pages for bpf_jit_[charge|uncharge]_modmem
> >>>>> bpf: use size instead of pages in bpf_binary_header
> >>>>> bpf: add a pointer of bpf_binary_header to bpf_prog
> >>>>> x86/alternative: introduce text_poke_jit
> >>>>> bpf: introduce bpf_prog_pack allocator
> >>>>> bpf, x86_64: use bpf_prog_pack allocator
> >>>>>
> >>>>> arch/x86/Kconfig                     |   1 +
> >>>>> arch/x86/include/asm/text-patching.h |   1 +
> >>>>> arch/x86/kernel/alternative.c        |  28 ++++
> >>>>> arch/x86/net/bpf_jit_comp.c          |  93 ++++++++++--
> >>>>> include/linux/bpf.h                  |   4 +-
> >>>>> include/linux/filter.h               |  23 ++-
> >>>>> kernel/bpf/core.c                    | 213 ++++++++++++++++++++++++---
> >>>>> kernel/bpf/trampoline.c              |   6 +-
> >>>>> 8 files changed, 328 insertions(+), 41 deletions(-)
> >>>>>
> >>>>> --
> >>>>> 2.30.2
> >>>
>