linux-kernel - Re: [GIT PULL v2] Networking for 6.7

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Date:   Thu, 9 Nov 2023 10:41:43 -0800
From:   Yonghong Song <yonghong.song@...ux.dev>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Hou Tao <houtao1@...wei.com>, Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [GIT PULL v2] Networking for 6.7


On 11/9/23 10:18 AM, Alexei Starovoitov wrote:
> On Thu, Nov 9, 2023 at 10:09 AM Yonghong Song <yonghong.song@...ux.dev> wrote:
>>
>> On 11/9/23 8:14 AM, Kirill A. Shutemov wrote:
>>> On Thu, Nov 09, 2023 at 08:01:39AM -0800, Alexei Starovoitov wrote:
>>>> On Thu, Nov 9, 2023 at 7:49 AM Kirill A. Shutemov <kirill@...temov.name> wrote:
>>>>> On Tue, Oct 31, 2023 at 02:09:48PM -0700, Jakub Kicinski wrote:
>>>>>>         bpf: Add support for non-fix-size percpu mem allocation
>>>>> Recent changes in BPF increased per-CPU memory consumption a lot.
>>>>>
>>>>> On virtual machine with 288 CPUs, per-CPU consumtion increased from 111 MB
>>>>> to 969 MB, or 8.7x.
>>>>>
>>>>> I've bisected it to the commit 41a5db8d8161 ("bpf: Add support for
>>>>> non-fix-size percpu mem allocation"), which part of the pull request.
>>>> Hmm. This is unexpected. Thank you for reporting.
>>>>
>>>> How did you measure this 111 MB vs 969 MB ?
>>>> Pls share the steps to reproduce.
>>> Boot VMM with 288 (qemu-system-x86_64 -smp 288) and check Percpu: field of
>>> /proc/meminfo.
>> I did some experiments with my VM. My VM currently supports up to 255 cpus,
>> so I tried 4/32/252 number of cpus. For a particular number of cpus, two
>> experiments are done:
>>     (1). bpf-percpu-mem-prefill
>>     (2). no-bpf-percpu-mem-prefill
>>
>> For 4 cpu:
>>      bpf-percpu-mem-prefill:
>>        Percpu:             2000 kB
>>      no-bpf-percpu-mem-prefill:
>>        Percpu:             1808 kB
>>
>>      bpf-percpu-mem-prefill percpu cost: (2000 - 1808)/4 KB = 48KB
>>
>> For 32 cpus:
>>      bpf-percpu-mem-prefill:
>>        Percpu:            25344 kB
>>      no-bpf-percpu-mem-prefill:
>>        Percpu:            14464 kB
>>
>>      bpf-percpu-mem-prefill percpu cost: (25344 - 14464)/4 KB = 340KB
>>
>> For 252 cpus:
>>      bpf-percpu-mem-prefill:
>>        Percpu:           230912 kB
>>      no-bpf-percpu-mem-prefill:
>>        Percpu:            57856 kB
>>
>>      bpf-percpu-mem-prefill percpu cost: (230912 - 57856)/4 KB = 686KB
>>
>> I am not able to reproduce the dramatic number from 111 MB to 969 MB.
>> My number with 252 cpus is from ~58MB to ~231MB.
> Even 231MB is way too much. We shouldn't be allocating that much.
> Let's switch to on-demand allocation. Only when bpf progs that
> user per-cpu are loaded.
Sounds good. Will craft a patch for this.