> -----Original Message-----
> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Varghese, Vipin
> Sent: Monday, November 26, 2018 4:15 AM
> To: Stephen Hemminger <step...@networkplumber.org>
> Cc: Pattan, Reshma <reshma.pat...@intel.com>; dev@dpdk.org;
> tho...@monjalon.net; Mcnamara, John <john.mcnam...@intel.com>;
> Byrne, Stephen1 <stephen1.by...@intel.com>; Glynn, Michael J
> <michael.j.gl...@intel.com>; Patel, Amol <amol.pa...@intel.com>
> Subject: Re: [dpdk-dev] [PATCH v4 5/9] app/procinfo: add support for show tm
>
> Hi Stephen,
>
> snipped
>
> >
> > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > > + if ((ret) | (!is_leaf))
> > > > > > > > > > > +
> > > > > > > > > >
> > > > > > > > > > Is the operator here should be || ?
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > Check is done for 'if either ret is not 0 or if it ret is
> > > > > > > > > 0 but not leaf' we skip leaf details print. If 'ret is 0 and
> > > > > > > > > is leaf'
> > > > > > > > > we skip continue to print
> > > > > > > > leaf details.
> > > > > > > >
> > > > > > > > IMO, using logical operator over bitwise operator is good
> > > > > > > > here in if statement
> > > > > > > .
> > > > > > > > Like below.?
> > > > > > > >
> > > > > > > > If (ret || (is_leaf == 0 ))
> > > > > > >
> > > > > > > Thanks for the information, if the logic is correct do I need
> > > > > > > to change for v6
> > > > > > >
> > > > > >
> > > > > > OK in v6, but you can wait to hear more comments from others if
> > > > > > any before sending v6 .
> > > > >
> > > > > Ok thanks Reshma, but can you tell me how the earlier logic fails
> > > > > and runs slow compared to logical or?
> > > >
> > > > Not about faster or slower.
> > >
> > > Now I see, I was wondering the suggestion was for improvement for
> > performance.
> > >
> > > >
> > > > Logical operators are commonly used in decision making in C programming.
> > > > Bitwise operators are used in C programming to perform bit-level
> > > > operations.
> > > >
> > >
> > > Agreed
> > >
> > > > Since , above if condition is for decision making here logical ||
> > > > operator will fit , so I am suggesting to use that.
> > > >
> > >
> > > But bitwise OR is not wrong right?
> > >
> > > > We don't need to do any bitwise manipulation in if condition to
> > > > make the decision, so bitwise | operator is not needed
> > >
> > > We can correct this in next patch set not v6 if this is only change for
> > > 'show tm'
> >
> > It could be that compiler might optimize logical into bitwise operation to
> > avoid
> > cost of conditional branch (if there are no side effects).
>
>
> Checking with 'EXTRA_CFLAGS=-g' we get the code generated as
>
> """
> if ((ret) | (!is_leaf))
> 9a512: 8b 85 28 fd ff ff mov eax,DWORD PTR [rbp-0x2d8]
> 9a518: 85 c0 test eax,eax
> 9a51a: 0f 94 c0 sete al
> 9a51d: 0f b6 c0 movzx eax,al
> 9a520: 0b 85 3c fd ff ff or eax,DWORD PTR [rbp-0x2c4]
> 9a526: 85 c0 test eax,eax
> 9a528: 75 74 jne 9a59e <show_tm+0x73e>
> continue;
> """
>
> Looks like the is_leaf is picked assembly 'test' is done then byte is set to
> 1 based on flags. This is then or with 'ret'. I think your observation is
> correct 'compiler is remapping to or'
If the operator is '|' what else except of 'OR' you expect it to be remapped?
Konstantin
