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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 19 Feb 2020 15:12:06 -0800
Message-ID: <CAADnVQJofPTYg73qoY6e-SwgyrtqPwU9JKx8DQ-9+L_uW6=X9g@mail.gmail.com>
Subject: Re: [PATCH v2 bpf] bpf: Do not grab the bucket spinlock by default on
 htab batch ops
To:     Yonghong Song <yhs@fb.com>
Cc:     Brian Vazquez <brianvv@google.com>,
        Brian Vazquez <brianvv.kernel@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S . Miller" <davem@davemloft.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>
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On Tue, Feb 18, 2020 at 1:23 PM Yonghong Song <yhs@fb.com> 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@fb.com>
> > Signed-off-by: Brian Vazquez <brianvv@google.com>
>
> Thanks for the fix.
> Acked-by: Yonghong Song <yhs@fb.com>

Applied. Thanks