Re: [PATCH v2] iio: adc: ad7944: Add support for "3-wire mode"

[David Lechner]

On Mon, Mar 18, 2024 at 8:10 AM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> On Mon, Mar 18, 2024 at 2:41 PM Jonathan Cameron
> <Jonathan.Cameron@xxxxxxxxxx> wrote:
> > > >  struct ad7944_adc {
> > > >     struct spi_device *spi;
> > > > +   enum ad7944_spi_mode spi_mode;
> > > >     /* Chip-specific timing specifications. */
> > > >     const struct ad7944_timing_spec *timing_spec;
> > > >     /* GPIO connected to CNV pin. */
> > > > @@ -58,6 +75,9 @@ struct ad7944_adc {
> > > >      } sample __aligned(IIO_DMA_MINALIGN);
> > > >  };
> > >
> > > Have you run `pahole` to see if there is a better place for a new member?
> >
> > I know this matters for structures where we see lots of them, but do we actually
> > care for one offs?  Whilst it doesn't matter here I'd focus much more
> > on readability and like parameter grouping for cases like this than wasting
> > a few bytes.
>
> This is _also_ true, but think more about cache line contamination.
> Even not-so-important bytes may decrease the performance. In some
> cases it's tolerable, in some it is not (high-speed ADC). In general I
> assume that the developer has to understand many aspects of the
> software and cache line contamination may be last but definitely not
> least.

Where could someone who doesn't know anything about cache line
contamination learn more about it? (searching the web for that phrase
doesn't turn up much)