Re: [PATCH bpf-next 0/2] bpf, riscv: use BPF prog pack allocator in BPF JIT

From: "Björn Töpel" <bjorn@kernel.org>
To: Puranjay Mohan <puranjay12@gmail.com>,
	paul.walmsley@sifive.com, palmer@dabbelt.com,
	aou@eecs.berkeley.edu, pulehui@huawei.com,
	conor.dooley@microchip.com, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
	yhs@fb.com, kpsingh@kernel.org, bpf@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Cc: puranjay12@gmail.com
Subject: Re: [PATCH bpf-next 0/2] bpf, riscv: use BPF prog pack allocator in BPF JIT
Date: Sun, 13 Aug 2023 22:27:54 +0200	[thread overview]
Message-ID: <87ttt21yd1.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <20230720154941.1504-1-puranjay12@gmail.com>

Puranjay Mohan <puranjay12@gmail.com> writes:

> 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.

Back in the saddle! Sorry for the horribly late reply...

Did you run the test_progs kselftest test, and passed w/o regressions? I
ran a test without/with your series (plus the patch from the arm64
series that you pointed out), and I'm getting regressions with this
series:

w/o Summary: 318/3114 PASSED, 27 SKIPPED, 60 FAILED
w/  Summary: 299/3026 PASSED, 33 SKIPPED, 79 FAILED

I'm did the test on commit 4c75bf7e4a0e ("Merge tag
'kbuild-fixes-v6.5-2' of
git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild").

I'm re-running, and investigating now.

Björn

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