Re: [RFC PATCH 0/3] enable bpf_prog_pack allocator for powerpc

[Hari Bathini <hbathini@linux.ibm.com>]

On 17/11/22 12:29 pm, Christophe Leroy wrote:
> 
> 
> Le 16/11/2022 à 18:01, Hari Bathini a écrit :
>>
>>
>> On 16/11/22 12:14 am, Christophe Leroy wrote:
>>>
>>>
>>> Le 14/11/2022 à 18:27, Christophe Leroy a écrit :
>>>>
>>>>
>>>> Le 14/11/2022 à 15:47, Hari Bathini a écrit :
>>>>> Hi Christophe,
>>>>>
>>>>> On 11/11/22 4:55 pm, Christophe Leroy wrote:
>>>>>> Le 10/11/2022 à 19:43, Hari Bathini a écrit :
>>>>>>> Most BPF programs are small, but they consume a page each. For
>>>>>>> systems
>>>>>>> with busy traffic and many BPF programs, this may also add
>>>>>>> significant
>>>>>>> pressure on instruction TLB. High iTLB pressure usually slows down
>>>>>>> the
>>>>>>> whole system causing visible performance degradation for production
>>>>>>> workloads.
>>>>>>>
>>>>>>> bpf_prog_pack, a customized allocator that packs multiple bpf
>>>>>>> programs
>>>>>>> into preallocated memory chunks, was proposed [1] to address it. This
>>>>>>> series extends this support on powerpc.
>>>>>>>
>>>>>>> Patches 1 & 2 add the arch specific functions needed to support this
>>>>>>> feature. Patch 3 enables the support for powerpc. The last patch
>>>>>>> ensures cleanup is handled racefully.
>>>>>>>
>>>>>
>>>>>>> Tested the changes successfully on a PowerVM. patch_instruction(),
>>>>>>> needed for bpf_arch_text_copy(), is failing for ppc32. Debugging it.
>>>>>>> Posting the patches in the meanwhile for feedback on these changes.
>>>>>>
>>>>>> I did a quick test on ppc32, I don't get such a problem, only
>>>>>> something
>>>>>> wrong in the dump print as traps intructions only are dumped, but
>>>>>> tcpdump works as expected:
>>>>>
>>>>> Thanks for the quick test. Could you please share the config you used.
>>>>> I am probably missing a few knobs in my conifg...
>>>>>
>>>>
>>>
>>> I also managed to test it on QEMU. The config is based on
>>> pmac32_defconfig.
>>
>> I had the same config but hit this problem:
>>
>>       # echo 1 > /proc/sys/net/core/bpf_jit_enable; modprobe test_bpf
>>       test_bpf: #0 TAX
>>       ------------[ cut here ]------------
>>       WARNING: CPU: 0 PID: 96 at arch/powerpc/net/bpf_jit_comp.c:367
>> bpf_int_jit_compile+0x8a0/0x9f8
> 
> I get no such problem, on QEMU, and I checked the .config has:

> CONFIG_STRICT_KERNEL_RWX=y
> CONFIG_STRICT_MODULE_RWX=y

Yeah. That did the trick. These options were missing in my config and
the pmac config you shared. I could not run the other config you shared
on QEMU. Thanks for all the pointers.

- Hari