Messages in this thread | | | Date | Mon, 7 Nov 2022 08:40:14 -0800 | Subject | Re: [PATCH bpf-next] bpf: Initialize same number of free nodes for each pcpu_freelist | From | Yonghong Song <> |
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On 11/7/22 12:50 AM, Xu Kuohai wrote: > From: Xu Kuohai <xukuohai@huawei.com> > > pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1 > free nodes for each CPU except the last initialized CPU, always making > the last CPU get fewer free nodes. For example, when nr_elems == 256
... free nodes for some cpus, and then possibly one cpu with fewer nodes, followed by remaining cpus with 0 nodes.
> and num_possible_cpus() == 32, if CPU 0 is the current cpu, CPU 0~27 > each gets 9 free nodes, CPU 28 gets 4 free nodes, CPU 29~31 get 0 free > nodes, while in fact each CPU should get 8 nodes equally. > > This patch initializes nr_elems / num_possible_cpus() free nodes for each > CPU firstly, and then allocates the remaining free nodes by one for each > CPU until no free nodes left. > > Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
LGTM. Did you observe any performance issues?
Acked-by: Yonghong Song <yhs@fb.com>
> --- > kernel/bpf/percpu_freelist.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c > index b6e7f5c5b9ab..89e84f7381cc 100644 > --- a/kernel/bpf/percpu_freelist.c > +++ b/kernel/bpf/percpu_freelist.c > @@ -100,12 +100,15 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size, > u32 nr_elems) > { > struct pcpu_freelist_head *head; > - int i, cpu, pcpu_entries; > + int i, cpu, pcpu_entries, remain_entries; > + > + pcpu_entries = nr_elems / num_possible_cpus(); > + remain_entries = nr_elems % num_possible_cpus(); > > - pcpu_entries = nr_elems / num_possible_cpus() + 1; > i = 0; > > for_each_possible_cpu(cpu) { > + int j = i + pcpu_entries + (remain_entries-- > 0 ? 1 : 0); > again: > head = per_cpu_ptr(s->freelist, cpu); > /* No locking required as this is not visible yet. */ > @@ -114,7 +117,7 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size, > buf += elem_size; > if (i == nr_elems) > break; > - if (i % pcpu_entries) > + if (i < j) > goto again; > } > }
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