[ofa-general] Re: [ewg] [PATCH] mlx4: remove limitation on LSO header size

[Roland Dreier]

 > >  > +	*blh = unlikely(halign > 64) ? 1 : 0;

 > > This idiom of "(boolean condition) ? 1 : 0" looks odd to me... doesn't
 > > (halign > 64) already evaluate to 1 or 0 anyway?  Does the unlikely()
 > > actually affect code generation here?

 > True, (halign > 64) is the same and is cleaner. As for the unlikely()
 > -- well it's already been there and besides, we're never sure if it
 > will improve anything so the same question could be asked for other
 > places in the code.

I was just wondering in this case where you are just assigning the
boolean value of the expression to a variable how unlikely affects
things.  I can understand for conditional jumps how the compiler can
choose to make the likely case more efficient, but when there are no
jumps then I was just curious how the hint could help.

 > > I assume this initialization is to avoid a compiler warning.  But the
 > > code is actually correct without initializing blh -- so I think that we
 > > save a tiny bit of code by doing uninitialized_var() instead?

 > We must initialize blh since it is used for any send request and not
 > just LSO opcodes. 

So then this patch was buggy because blh was not reinitialized as we
loop through multiple work requests?  eg an LSO request followed by a
non-LSO request?

Anyway I'll look over the newer patch.