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Message-ID: <87pm3qt2c8.fsf@all.your.base.are.belong.to.us>
Date: Mon, 14 Aug 2023 11:12:07 +0200
From: Björn Töpel <bjorn@...nel.org>
To: Puranjay Mohan <puranjay12@...il.com>, paul.walmsley@...ive.com,
palmer@...belt.com, aou@...s.berkeley.edu, pulehui@...wei.com,
conor.dooley@...rochip.com, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
yhs@...com, kpsingh@...nel.org, bpf@...r.kernel.org,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: puranjay12@...il.com
Subject: Re: [PATCH bpf-next 0/2] bpf, riscv: use BPF prog pack allocator in
BPF JIT
Puranjay Mohan <puranjay12@...il.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.
>
> 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 (2):
> riscv: Extend patch_text_nosync() for multiple pages
> bpf, riscv: use prog pack allocator in the BPF JIT
I get a hang for "test_tag", but it's not directly related to your
series, but rather "remote fence.i".
| rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
| rcu: 0-....: (1400 ticks this GP) idle=d5e4/1/0x4000000000000000 softirq=5542/5542 fqs=1862
| rcu: (detected by 1, t=5252 jiffies, g=10253, q=195 ncpus=4)
| Task dump for CPU 0:
| task:kworker/0:5 state:R running task stack:0 pid:319 ppid:2 flags:0x00000008
| Workqueue: events bpf_prog_free_deferred
| Call Trace:
| [<ffffffff80cbc444>] __schedule+0x2d0/0x940
| watchdog: BUG: soft lockup - CPU#0 stuck for 21s! [kworker/0:5:319]
| Modules linked in: nls_iso8859_1 drm fuse i2c_core drm_panel_orientation_quirks backlight dm_mod configfs ip_tables x_tables
| CPU: 0 PID: 319 Comm: kworker/0:5 Not tainted 6.5.0-rc5 #1
| Hardware name: riscv-virtio,qemu (DT)
| Workqueue: events bpf_prog_free_deferred
| epc : __sbi_rfence_v02_call.isra.0+0x74/0x11a
| ra : __sbi_rfence_v02+0xda/0x1a4
| epc : ffffffff8000ab4c ra : ffffffff8000accc sp : ff20000001c9bbd0
| gp : ffffffff82078c48 tp : ff600000888e6a40 t0 : ff20000001c9bd44
| t1 : 0000000000000000 t2 : 0000000000000040 s0 : ff20000001c9bbf0
| s1 : 0000000000000010 a0 : 0000000000000000 a1 : 0000000000000000
| a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
| a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43
| s2 : 000000000000ffff s3 : 00000000ffffffff s4 : ffffffff81667528
| s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
| s8 : 0000000000000001 s9 : 0000000000000003 s10: 0000000000000040
| s11: ffffffff8207d240 t3 : 000000000000000f t4 : 000000000000002a
| t5 : ff600000872df140 t6 : ffffffff81e26828
| status: 0000000200000120 badaddr: 0000000000000000 cause: 8000000000000005
| [<ffffffff8000ab4c>] __sbi_rfence_v02_call.isra.0+0x74/0x11a
| [<ffffffff8000accc>] __sbi_rfence_v02+0xda/0x1a4
| [<ffffffff8000a886>] sbi_remote_fence_i+0x1e/0x26
| [<ffffffff8000cee2>] flush_icache_all+0x1a/0x48
| [<ffffffff80007736>] patch_text_nosync+0x6c/0x8c
| [<ffffffff8000f0f8>] bpf_arch_text_invalidate+0x62/0xac
| [<ffffffff8016c538>] bpf_prog_pack_free+0x9c/0x1b2
| [<ffffffff8016c84a>] bpf_jit_binary_pack_free+0x20/0x4a
| [<ffffffff8000f198>] bpf_jit_free+0x56/0x9e
| [<ffffffff8016b43a>] bpf_prog_free_deferred+0x15a/0x182
| [<ffffffff800576c4>] process_one_work+0x1b6/0x3d6
| [<ffffffff80057d52>] worker_thread+0x84/0x378
| [<ffffffff8005fc2c>] kthread+0xe8/0x108
| [<ffffffff80003ffa>] ret_from_fork+0xe/0x20
I'm digging into that now, and I would appreciate if you could run the
test_tag on VF2 or similar (I'm missing that HW).
It seems like we're hitting a bug with this series, so let's try to
figure out where the problems is, prior merging it.
Björn
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