Re: [PATCH v2 bpf] bpf: Do not grab the bucket spinlock by default on htab batch ops

[Alexei Starovoitov]

On Tue, Feb 18, 2020 at 1:23 PM Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 2/18/20 9:25 AM, Brian Vazquez wrote:
> > Grabbing the spinlock for every bucket even if it's empty, was causing
> > significant perfomance cost when traversing htab maps that have only a
> > few entries. This patch addresses the issue by checking first the
> > bucket_cnt, if the bucket has some entries then we go and grab the
> > spinlock and proceed with the batching.
> >
> > Tested with a htab of size 50K and different value of populated entries.
> >
> > Before:
> >    Benchmark             Time(ns)        CPU(ns)
> >    ---------------------------------------------
> >    BM_DumpHashMap/1       2759655        2752033
> >    BM_DumpHashMap/10      2933722        2930825
> >    BM_DumpHashMap/200     3171680        3170265
> >    BM_DumpHashMap/500     3639607        3635511
> >    BM_DumpHashMap/1000    4369008        4364981
> >    BM_DumpHashMap/5k     11171919       11134028
> >    BM_DumpHashMap/20k    69150080       69033496
> >    BM_DumpHashMap/39k   190501036      190226162
> >
> > After:
> >    Benchmark             Time(ns)        CPU(ns)
> >    ---------------------------------------------
> >    BM_DumpHashMap/1        202707         200109
> >    BM_DumpHashMap/10       213441         210569
> >    BM_DumpHashMap/200      478641         472350
> >    BM_DumpHashMap/500      980061         967102
> >    BM_DumpHashMap/1000    1863835        1839575
> >    BM_DumpHashMap/5k      8961836        8902540
> >    BM_DumpHashMap/20k    69761497       69322756
> >    BM_DumpHashMap/39k   187437830      186551111
> >
> > Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map")
> > Cc: Yonghong Song <yhs@xxxxxx>
> > Signed-off-by: Brian Vazquez <brianvv@xxxxxxxxxx>
>
> Thanks for the fix.
> Acked-by: Yonghong Song <yhs@xxxxxx>

Applied. Thanks