Messages in this thread | | | From | Alexei Starovoitov <> | Date | Thu, 9 Nov 2023 10:18:44 -0800 | Subject | Re: [GIT PULL v2] Networking for 6.7 |
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On Thu, Nov 9, 2023 at 10:09 AM Yonghong Song <yonghong.song@linux.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@shutemov.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.
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