Re: [GIT PULL v2] Networking for 6.7

[Yonghong Song]

On 11/9/23 10:18 AM, Alexei Starovoitov wrote:
> On Thu, Nov 9, 2023 at 10:09 AM Yonghong Song <yonghong.song@xxxxxxxxx> 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@xxxxxxxxxxxxx> 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.