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Date:	Mon, 11 May 2015 13:31:23 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	linux-kernel@...r.kernel.org
Subject: RE: softirq under reporting with CONFIG_NO_HZ_* and under syn flood
 ?

Hello,

I can confirm that I'm also observing the same issue. Here is the output 
of turbostat:

without hping running (Most of the time is spent in idle C6 state, which 
is expected):

pk cor CPU    %c0  GHz  TSC SMI    %c1    %c3    %c6    %c7 CTMP PTMP   
%pc2   %pc3   %pc6   %pc7  Pkg_W  Cor_W RAM_W PKG_% RAM_%
                        0.02 1.77 2.10   0   0.09   0.00  99.89 0.00   
54   53   6.45   0.00  93.05   0.00  15.93   1.25  5.90 0.00  0.00
  0   0   0         0.02 1.81 2.10   0   0.05   0.00  99.92   0.00 47   
47   6.53   0.00  93.00   0.00   7.86   0.57  4.22  0.00  0.00
  0   0  12        0.01 1.48 2.10   0   0.07
  0   1   1         0.05 1.46 2.10   0   0.18   0.00  99.77   0.00 47
  0   1  13        0.01 1.56 2.10   0   0.22
  0   2   2         0.01 1.61 2.10   0   0.06   0.00  99.93   0.00 47
  0   2  14        0.02 1.81 2.10   0   0.05
  0   3   3         0.03 1.92 2.10   0   0.04   0.00  99.93   0.00 47
  0   3  15        0.01 1.60 2.10   0   0.07
  0   4   4         0.01 1.60 2.10   0   0.06   0.00  99.93   0.00 47
  0   4  16        0.01 1.61 2.10   0   0.06
  0   5   5         0.01 1.57 2.10   0   0.03   0.00  99.96   0.00 47
  0   5  17        0.00 1.62 2.10   0   0.03
  1   0   6         0.01 1.66 2.10   0   0.03   0.00  99.96   0.00 51   
53   6.37   0.00  93.10   0.00   8.07   0.67  1.68  0.00  0.00
  1   0  18        0.01 1.57 2.10   0   0.04
  1   1   7         0.03 1.44 2.10   0   0.10   0.00  99.87   0.00 51
  1   1  19        0.00 1.62 2.10   0   0.13
  1   2   8         0.01 1.64 2.10   0   0.06   0.00  99.94   0.00 51
  1   2  20        0.01 1.41 2.10   0   0.05
  1   3   9         0.03 1.57 2.10   0   0.11   0.00  99.86   0.00 51
  1   3  21        0.01 1.49 2.10   0   0.13
  1   4  10        0.20 2.04 2.10   0   0.08   0.00  99.72   0.00 51
  1   4  22        0.01 1.49 2.10   0   0.27
  1   5  11        0.01 1.66 2.10   0   0.11   0.00  99.88   0.00 54
  1   5  23        0.02 1.71 2.10   0   0.10


And with hping running as per your email:

pk cor CPU    %c0  GHz  TSC SMI    %c1    %c3    %c6    %c7 CTMP PTMP   
%pc2   %pc3   %pc6   %pc7  Pkg_W  Cor_W RAM_W PKG_% RAM_%
                     10.91 2.10 2.10   0  36.57   0.75  51.77 0.00   
59   59  49.50   0.13   0.86   0.00  46.39  22.55  5.49 0.00  0.00
  0   0   0       0.10 2.07 2.10   0  94.47   1.68   3.76   0.00 56   
59   0.66   0.27   0.71   0.00  28.70  16.90  3.85  0.00  0.00
  0   0  12      31.26 2.10 2.10   0  63.31
  0   1   1       33.87 2.10 2.10   0  61.20   1.58   3.35   0.00 55
  0   1  13      33.87 2.10 2.10   0  61.20
  0   2   2      33.77 2.10 2.10   0  61.59   1.42   3.22   0.00   56
  0   2  14      33.95 2.10 2.10   0  61.42
  0   3   3      31.66 2.10 2.10   0  63.25   1.37   3.72   0.00   52
  0   3  15       0.03 2.01 2.10   0  94.88
  0   4   4      31.59 2.10 2.10   0  62.80   1.47   4.14   0.00   59
  0   4  16       0.03 2.01 2.10   0  94.36
  0   5   5      31.21 2.10 2.10   0  63.43   1.50   3.86   0.00   57
  0   5  17       0.03 2.00 2.10   0  94.61
  1   0   6       0.04 1.72 2.10   0   0.08   0.00  99.88   0.00 55   
58  98.33   0.00   1.00   0.00  17.70   5.65  1.64  0.00  0.00
  1   0  18       0.01 1.47 2.10   0   0.11
  1   1   7       0.02 1.53 2.10   0   0.05   0.00  99.94   0.00   52
  1   1  19       0.01 1.43 2.10   0   0.06
  1   2   8       0.01 1.49 2.10   0   0.04   0.00  99.95   0.00   58
  1   2  20       0.01 1.31 2.10   0   0.04
  1   3   9       0.04 1.59 2.10   0   0.09   0.00  99.88   0.00   51
  1   3  21       0.01 1.41 2.10   0   0.11
  1   4  10       0.22 2.04 2.10   0   0.09   0.00  99.69   0.00   53
  1   4  22       0.01 1.54 2.10   0   0.30
  1   5  11       0.06 1.91 2.10   0   0.10   0.00  99.84   0.00   52
  1   5  23       0.02 1.49 2.10   0   0.15

Which clearly shows that the processor spent some time to process the 
syn flood packets, however
"top" reported the cpu usage at 0%. My kernel version is v4.0



View attachment "kernel-conf" of type "text/plain" (93646 bytes)

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