Re: [PATCH v5 bpf-next 0/5] bpf_prog_pack followup

[Song Liu <songliubraving@fb.com>]

oops, wrong address for x86@. 

CC x86@kernel.org

> On Jun 24, 2022, at 2:57 PM, Song Liu <song@kernel.org> wrote:
> 
> This set is the second half of v4 [1].
> 
> Changes v4 => v5:
> 1. Rebase and resolve conflicts due to module.c split.
> 2. Update experiment results (below).
> 
> For our web service production benchmark, bpf_prog_pack on 4kB pages
> gives 0.5% to 0.7% more throughput than not using bpf_prog_pack.
> bpf_prog_pack on 2MB pages 0.6% to 0.9% more throughput than not using
> bpf_prog_pack. Note that 0.5% is a huge improvement for our fleet. I
> believe this is also significant for other companies with many thousand
> servers.
> 
> Update: Further experiments (suggested by Rick Edgecombe) showed that most
> of benefit on the web service benchmark came from less direct map
> fragmentation. The experiment is as follows:
> 
> Side A: 2MB bpf prog pack on a single 2MB page;
> Side B: 2MB bpf prog pack on 512x 4kB pages;
> 
> The system only uses about 200kB for BPF programs, but 2MB is allocated
> for bpf_prog_pack (for both A and B). Therefore, direct map fragmentation
> caused by BPF programs is elminated, and we are only measuring the
> performance difference of 1x 2MB page vs. ~50 4kB pages (we only use
> about 50 out of the 512 pages). For these two sides, the difference in
> system throughput is within the noise. I also measured iTLB-load-misses
> caused by bpf programs, which is ~300/s for case A, and ~1600/s for case B.
> The overall iTLB-load-misses is about 1.5M/s on these hosts. Therefore,
> we can clearly see 2MB page reduces iTLB misses, but the difference is not
> enough to have visible impact on system throughput.
> 
> Of course, the impact of iTLB miss will be more significant for systems
> with more BPF programs loaded.
> 
> [1] https://lore.kernel.org/bpf/20220520235758.1858153-1-song@kernel.org/
> 
> Song Liu (5):
>  module: introduce module_alloc_huge
>  bpf: use module_alloc_huge for bpf_prog_pack
>  vmalloc: WARN for set_vm_flush_reset_perms() on huge pages
>  vmalloc: introduce huge_vmalloc_supported
>  bpf: simplify select_bpf_prog_pack_size
> 
> arch/x86/kernel/module.c     | 21 +++++++++++++++++++++
> include/linux/moduleloader.h |  5 +++++
> include/linux/vmalloc.h      |  7 +++++++
> kernel/bpf/core.c            | 25 ++++++++++---------------
> kernel/module/main.c         |  8 ++++++++
> mm/vmalloc.c                 |  5 +++++
> 6 files changed, 56 insertions(+), 15 deletions(-)
> 
> --
> 2.30.2