Re: [PATCH bpf-next v3 0/3] bpf, riscv: use BPF prog pack allocator in BPF JIT

["Björn Töpel" <bjorn@kernel.org>]

Puranjay Mohan <puranjay12@gmail.com> writes:

> Changes in v2 -> v3:
> 1. Fix maximum width of code in patches from 80 to 100. [All patches]
> 2. Add checks for ctx->ro_insns == NULL. [Patch 3]
> 3. Fix check for edge condition where amount of text to set > 2 * pagesize
>    [Patch 1 and 2]
> 4. Add reviewed-by in patches.
> 5. Adding results of selftest here:
>    Using the command: ./test_progs on qemu
>    Without the series: Summary: 336/3162 PASSED, 56 SKIPPED, 90 FAILED
>    With this series: Summary: 336/3162 PASSED, 56 SKIPPED, 90 FAILED
>
> Changes in v1 -> v2:
> 1. Implement a new function patch_text_set_nosync() to be used in bpf_arch_text_invalidate().
>    The implementation in v1 called patch_text_nosync() in a loop and it was bad as it would
>    call flush_icache_range() for every word making it really slow. This was found by running
>    the test_tag selftest which would take forever to complete.
>
> Here is some data to prove the V2 fixes the problem:
>
> Without this series:
> root@rv-selftester:~/src/kselftest/bpf# time ./test_tag
> test_tag: OK (40945 tests)
>
> real    7m47.562s
> user    0m24.145s
> sys     6m37.064s
>
> With this series applied:
> root@rv-selftester:~/src/selftest/bpf# time ./test_tag
> test_tag: OK (40945 tests)
>
> real    7m29.472s
> user    0m25.865s
> sys     6m18.401s
>
> BPF programs currently consume a page each on RISCV. For systems with many BPF
> programs, this adds significant pressure to instruction TLB. High iTLB pressure
> usually causes slow down for the whole system.
>
> Song Liu introduced the BPF prog pack allocator[1] to mitigate the above issue.
> It packs multiple BPF programs into a single huge page. It is currently only
> enabled for the x86_64 BPF JIT.
>
> I enabled this allocator on the ARM64 BPF JIT[2]. It is being reviewed now.
>
> This patch series enables the BPF prog pack allocator for the RISCV BPF JIT.
> This series needs a patch[3] from the ARM64 series to work.
>
> ======================================================
> Performance Analysis of prog pack allocator on RISCV64
> ======================================================
>
> Test setup:
> ===========
>
> Host machine: Debian GNU/Linux 11 (bullseye)
> Qemu Version: QEMU emulator version 8.0.3 (Debian 1:8.0.3+dfsg-1)
> u-boot-qemu Version: 2023.07+dfsg-1
> opensbi Version: 1.3-1
>
> To test the performance of the BPF prog pack allocator on RV, a stresser
> tool[4] linked below was built. This tool loads 8 BPF programs on the system and
> triggers 5 of them in an infinite loop by doing system calls.
>
> The runner script starts 20 instances of the above which loads 8*20=160 BPF
> programs on the system, 5*20=100 of which are being constantly triggered.
> The script is passed a command which would be run in the above environment.
>
> The script was run with following perf command:
> ./run.sh "perf stat -a \
>         -e iTLB-load-misses \
>         -e dTLB-load-misses  \
>         -e dTLB-store-misses \
>         -e instructions \
>         --timeout 60000"
>
> The output of the above command is discussed below before and after enabling the
> BPF prog pack allocator.
>
> The tests were run on qemu-system-riscv64 with 8 cpus, 16G memory. The rootfs
> was created using Bjorn's riscv-cross-builder[5] docker container linked below.
>
> Results
> =======
>
> Before enabling prog pack allocator:
> ------------------------------------
>
> Performance counter stats for 'system wide':
>
>            4939048      iTLB-load-misses
>            5468689      dTLB-load-misses
>             465234      dTLB-store-misses
>      1441082097998      instructions
>
>       60.045791200 seconds time elapsed
>
> After enabling prog pack allocator:
> -----------------------------------
>
> Performance counter stats for 'system wide':
>
>            3430035      iTLB-load-misses
>            5008745      dTLB-load-misses
>             409944      dTLB-store-misses
>      1441535637988      instructions
>
>       60.046296600 seconds time elapsed
>
> Improvements in metrics
> =======================
>
> It was expected that the iTLB-load-misses would decrease as now a single huge
> page is used to keep all the BPF programs compared to a single page for each
> program earlier.
>
> --------------------------------------------
> The improvement in iTLB-load-misses: -30.5 %
> --------------------------------------------
>
> I repeated this expriment more than 100 times in different setups and the
> improvement was always greater than 30%.
>
> This patch series is boot tested on the Starfive VisionFive 2 board[6].
> The performance analysis was not done on the board because it doesn't
> expose iTLB-load-misses, etc. The stresser program was run on the board to test
> the loading and unloading of BPF programs
>
> [1] https://lore.kernel.org/bpf/20220204185742.271030-1-song@kernel.org/
> [2] https://lore.kernel.org/all/20230626085811.3192402-1-puranjay12@gmail.com/
> [3] https://lore.kernel.org/all/20230626085811.3192402-2-puranjay12@gmail.com/
> [4] https://github.com/puranjaymohan/BPF-Allocator-Bench
> [5] https://github.com/bjoto/riscv-cross-builder
> [6] https://www.starfivetech.com/en/site/boards
>
> Puranjay Mohan (3):
>   riscv: extend patch_text_nosync() for multiple pages
>   riscv: implement a memset like function for text
>   bpf, riscv: use prog pack allocator in the BPF JIT

Thank you! For the series:

Acked-by: Björn Töpel <bjorn@kernel.org>
Tested-by: Björn Töpel <bjorn@rivosinc.com>

@Alexei @Daniel This series depends on a core BPF patch from the Arm
                series [3].

@Palmer LMK if you have any concerns taking the RISC-V text patching
        stuff via the BPF tree.


Björn