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

Puranjay Mohan
2023-08-14T09:43:05Z

Hi Björn,

On Mon, Aug 14, 2023 at 11:12 AM Björn Töpel <bjorn@kernel.org> wrote:
>
> 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.
> >
> > 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".

I was seeing some stalls like this even without my series but couldn't
debug them at that time.

>
> | 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).

Sure, I will try to run this on the board.
I will rebase my series(+ the patch from arm64 series) on the latest
bpf-next tree and try to run it.
Let me know if I need to add:
+ select HAVE_EFFICIENT_UNALIGNED_ACCESS if MMU && 64BIT

>
> 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

Thanks,
Puranjay