回复：RE: [vpp-dev] Why not break the check flow when the first error occurs of ip4_inout()?

远志 <i...@leenzhu.com> Tue, 21 Jul 2020 17:57:24 -0700

Hi Dave,


Thanks for your reply.




------------------&nbsp;????????&nbsp;------------------
??????:                                                                         
                                               "Dave Barach (dbarach)"          
                                                                          
<dbar...@cisco.com&gt;;
????????:&nbsp;2020??7??21??(??????) ????7:12
??????:&nbsp;"????"<i...@leenzhu.com&gt;;"vpp-dev"<vpp-dev@lists.fd.io&gt;;

????:&nbsp;RE: [vpp-dev] Why not break the check flow when the first error 
occurs of ip4_inout()?



  
Branches hurt performance more than arithmetic and/or conditional moves. 
 
&nbsp;
  
From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io&gt; On Behalf Of "??
 Sent: Monday, July 20, 2020 10:17 PM
 To: vpp-dev <vpp-dev@lists.fd.io&gt;
 Subject: [vpp-dev] Why not break the check flow when the first error occurs of 
ip4_inout()?
 
 
&nbsp;
  
Hi all,
 
  
&nbsp;
 
  
When I'm reading the ip4_input.c code, I'm confused about the following code.
 
  
&nbsp;
 
   
vnet/vnet/ip/ip4_input.c:ip4_input_inline()
 
  
{
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;...
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = error1 = IP4_ERROR_NONE;
 
  
&nbsp;
 
   
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* Punt packets with options. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = 
(ip0-&gt;ip_version_and_header_length &amp; 0xf) != 5 ? IP4_ERROR_OPTIONS : 
error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = 
(ip1-&gt;ip_version_and_header_length &amp; 0xf) != 5 ? IP4_ERROR_OPTIONS : 
error1;
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* Version != 4?&nbsp; Drop it. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = 
(ip0-&gt;ip_version_and_header_length &gt;&gt; 4) != 4 ? IP4_ERROR_VERSION : 
error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = 
(ip1-&gt;ip_version_and_header_length &gt;&gt; 4) != 4 ? IP4_ERROR_VERSION : 
error1;
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* Verify header checksum. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ....
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = 0xffff != ip_csum_fold 
(sum0) ? IP4_ERROR_BAD_CHECKSUM : error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = 0xffff != ip_csum_fold 
(sum1) ? IP4_ERROR_BAD_CHECKSUM : error1;
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* Drop fragmentation offset 1 
packets. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ....
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = ip4_get_fragment_offset 
(ip0) == 1 ? IP4_ERROR_FRAGMENT_OFFSET_ONE : error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = ip4_get_fragment_offset 
(ip1) == 1 ? IP4_ERROR_FRAGMENT_OFFSET_ONE : error1;
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* TTL < 1? Drop it. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = (ip0-&gt;ttl < 1 &amp;&amp; 
cast0 == VNET_UNICAST) ? IP4_ERROR_TIME_EXPIRED : error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = (ip1-&gt;ttl < 1 &amp;&amp; 
cast1 == VNET_UNICAST) ? IP4_ERROR_TIME_EXPIRED : error1;
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; /* Verify lengths. */
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error0 = ip_len0 < sizeof (ip0[0]) ? 
IP4_ERROR_TOO_SHORT : error0;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error1 = ip_len1 < sizeof (ip1[0]) ? 
IP4_ERROR_TOO_SHORT : error1;
 
 
   
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; p0-&gt;error = 
error_node-&gt;errors[error0];
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; p1-&gt;error = 
error_node-&gt;errors[error1];
 
  
&nbsp;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (PREDICT_FALSE(error0 != 
IP4_ERROR_NONE))
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (error0 == 
IP4_ERROR_TIME_EXPIRED) {
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
icmp4_error_set_vnet_buffer(p0, ICMP4_time_exceeded,
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp; ICMP4_time_exceeded_ttl_exceeded_in_transit, 0);
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next0 = 
IP4_INPUT_NEXT_ICMP_ERROR;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next0 = 
error0 != IP4_ERROR_OPTIONS ? IP4_INPUT_NEXT_DROP : IP4_INPUT_NEXT_PUNT;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (PREDICT_FALSE(error1 != 
IP4_ERROR_NONE))
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; {
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (error1 == 
IP4_ERROR_TIME_EXPIRED) {
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
icmp4_error_set_vnet_buffer(p1, ICMP4_time_exceeded,
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 
&nbsp; &nbsp; &nbsp; ICMP4_time_exceeded_ttl_exceeded_in_transit, 0);
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next1 = 
IP4_INPUT_NEXT_ICMP_ERROR;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; next1 = 
error1 != IP4_ERROR_OPTIONS ? IP4_INPUT_NEXT_DROP : IP4_INPUT_NEXT_PUNT;
 
  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }
 
 
  
}
 
 
  
&nbsp;
 
  
-----------------------------------------------------------------------------------------------
 
  
&nbsp;
 
  
1. why not break the check flow when the first error occurs? for example:
 
  
&nbsp; &nbsp; &nbsp;error0 = (ip0-&gt;ip_version_and_header_length &amp; 0xf) 
!= 5 ? IP4_ERROR_OPTIONS : error0;
 
  
&nbsp; &nbsp; &nbsp;if (error0 != IP4_ERROR_NONE) {goto error_handle;}
 
  
&nbsp;
 
  
2. suppose all the results of checking are wrong, I think at the end, we could 
only get the last error rather than the first error.
 
  
&nbsp; &nbsp; &nbsp;options error, version error, ...and length error, so the 
last error is IP4_ERROR_TOO_SHORT
 
  
&nbsp;
 
  
Is there any optimization concept behind this?? Can I improe(hope it will 
improve :-)?? the code like the following, before we check the next error,  
let's check wether the error has occured:
 
  
&nbsp;
 
  
&nbsp; /* init error to none */
 
  
&nbsp; error0 = error1 = IP4_ERROR_NONE;
 
  
&nbsp;
 
  
&nbsp; /* check the first error */
 
  
&nbsp; error0 = (ip0-&gt;ip_version_and_header_length &amp; 0xf) != 5 ? 
IP4_ERROR_OPTIONS : error0;
 
  
&nbsp;
 
  
&nbsp; error0 = error0 != IP4_ERROR_NONE? error0 : 
((ip0-&gt;ip_version_and_header_length &gt;&gt; 4) != 4 ? IP4_ERROR_VERSION : 
error0);
 
  
&nbsp; error0 = error0 != IP4_ERROR_NONE? error0 : (0xffff != ip_csum_fold 
(sum0) ? IP4_ERROR_BAD_CHECKSUM : error0);
 
  
&nbsp; ...
 
  
&nbsp;
 
  
&nbsp;

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回复：RE: [vpp-dev] Why not break the check flow when the first error occurs of ip4_inout()?

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