Re: [PATCH] bpf: test_run: reduce kernel stack usage

[David Laight]

On Fri, 15 May 2026 19:38:04 +0100
David Laight <david.laight.linux@xxxxxxxxx> wrote:

> On Fri, 15 May 2026 17:15:46 +0200
> "Arnd Bergmann" <arnd@xxxxxxxx> wrote:
> 
> > On Fri, May 15, 2026, at 16:47, Alexei Starovoitov wrote:  
> > > On Fri, May 15, 2026 at 4:31 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> > >
> > > 1k?
> > > pahole -C xdp_test_data
> > > /* size: 192, cachelines: 3, members: 9 */
> > > /* sum members: 120, holes: 1, sum holes: 56 */
> > > /* padding: 16 */
> > > /* paddings: 1, sum paddings: 36 */
> > >
> > > what s390 doing to make it huge?    
> > 
> > I think it's a combination of cacheline alignment (256 byte
> > lines) that leads to padding before 'rxq' and at the end of
> > xdp_test_data, as well as CONFIG_KASAN_STACK that increases
> > the stack usage further.  
> 
> There will also be a 'double stack frame' in order to put an
> aligned item on stack.
> That could be slightly larger than a stack frame and probably doesn't
                                       ^ cache line
> show up in the figures.
> 
> -- David
>