Hi Mark,
On 6/26/23 10:58 AM, Puranjay Mohan wrote:
BPF programs currently consume a page each on ARM64. 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.
This patch series enables the BPF prog pack allocator for the ARM64 BPF JIT.
====================================================
Performance Analysis of prog pack allocator on ARM64
====================================================
To test the performance of the BPF prog pack allocator on ARM64, a stresser
tool[2] 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.
In the above environment we try to build Python-3.8.4 and try to find different
iTLB metrics for the compilation done by gcc-12.2.0.
The source code[3] is configured with the following command:
./configure --enable-optimizations --with-ensurepip=install
Then the runner script is executed with the following command:
./run.sh "perf stat -e ITLB_WALK,L1I_TLB,INST_RETIRED,iTLB-load-misses -a make -j32"
This builds Python while 160 BPF programs are loaded and 100 are being constantly
triggered and measures iTLB related metrics.
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-aarch64 with 32 cpus, 4G memory, -machine virt,
-cpu host, and -enable-kvm.
Results
-------
Before enabling prog pack allocator:
------------------------------------
Performance counter stats for 'system wide':
333278635 ITLB_WALK
6762692976558 L1I_TLB
25359571423901 INST_RETIRED
15824054789 iTLB-load-misses
189.029769053 seconds time elapsed
After enabling prog pack allocator:
-----------------------------------
Performance counter stats for 'system wide':
190333544 ITLB_WALK
6712712386528 L1I_TLB
25278233304411 INST_RETIRED
5716757866 iTLB-load-misses
185.392650561 seconds time elapsed
Improvements in metrics
-----------------------
Compilation time ---> 1.92% faster
iTLB-load-misses/Sec (Less is better) ---> 63.16% decrease
ITLB_WALK/1000 INST_RETIRED (Less is better) ---> 42.71% decrease
ITLB_Walk/L1I_TLB (Less is better) ---> 42.47% decrease
[1] https://lore.kernel.org/bpf/20220204185742.271030-1-song@xxxxxxxxxx/
[2] https://github.com/puranjaymohan/BPF-Allocator-Bench
[3] https://www.python.org/ftp/python/3.8.4/Python-3.8.4.tgz
Chanes in V3 => V4: Changes only in 3rd patch
1. Fix the I-cache maintenance: Clean the data cache and invalidate the i-Cache
only *after* the instructions have been copied to the ROX region.
If you get a chance to take another look at the v4 changes from Puranjay and
in case they look good to you reply with an Ack, that would be great.
Thanks,
Daniel
