Re: [PATCH 1/6] s390/ctcm: Put struct th_header and th_sweep on stack.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2020-11-19 09:45:08 [+0200], Julian Wiedmann wrote:
> On 18.11.20 12:53, Sebastian Andrzej Siewior wrote:
> > The size of struct th_header is 8 byte and the size of struct th_sweep
> > is 16 byte. The memory for is allocated, initialized, used and
> > deallocated a few lines later.
> > 
> > It is more efficient to avoid the allocation/free dance and keeping the
> > variable on stack. Especially since the compiler is smart enough to not
> > allocate the memory on stack but assign the values directly.
> > 
> > Declare struct th_sweep/th_header on stack and initialize it to zero.
> > Use the local variable instead of the pointer.
> > 
> 
> Frankly, I'd much rather see us use the pointers that are returned from
> skb_push() and skb_put(). No need for the on-stack & memcpy indirection.

You are aware that the compiler optimizes the on-stack memory away and
you get the zero-init for free due to the way the assignment is made?
There is no memcpy() in the resulting code.

Sebastian