Re: [dpdk-dev] [PATCH v3 1/4] eal: Introduce new cache macro definitions

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Mon, Jan 04, 2016 at 02:15:53PM +0100, Olivier MATZ wrote:
> Hi Jerin,

Hi Olivier,

> 
> Please see some comments below.
> 
> On 12/14/2015 05:32 AM, Jerin Jacob wrote:
> > - RTE_CACHE_MIN_LINE_SIZE(Supported minimum cache line size)
> > - __rte_cache_min_aligned(Force minimum cache line alignment)
> > - RTE_CACHE_LINE_SIZE_LOG2(Express cache line size in terms of log2)
> > 
> > Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > Suggested-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> > ---
> >  lib/librte_eal/common/include/rte_memory.h | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/lib/librte_eal/common/include/rte_memory.h b/lib/librte_eal/common/include/rte_memory.h
> > index 9c9e40f..b67a76f 100644
> > --- a/lib/librte_eal/common/include/rte_memory.h
> > +++ b/lib/librte_eal/common/include/rte_memory.h
> > @@ -77,11 +77,27 @@ enum rte_page_sizes {
> >  	(RTE_CACHE_LINE_SIZE * ((size + RTE_CACHE_LINE_SIZE - 1) / RTE_CACHE_LINE_SIZE))
> >  /**< Return the first cache-aligned value greater or equal to size. */
> >  
> > +/**< Cache line size in terms of log2 */
> > +#if RTE_CACHE_LINE_SIZE == 64
> > +#define RTE_CACHE_LINE_SIZE_LOG2 6
> > +#elif RTE_CACHE_LINE_SIZE == 128
> > +#define RTE_CACHE_LINE_SIZE_LOG2 7
> > +#else
> > +#error "Unsupported cache line size"
> > +#endif
> > +
> > +#define RTE_CACHE_MIN_LINE_SIZE 64	/**< Minimum Cache line size. */
> > +
> 
> I think RTE_CACHE_LINE_MIN_SIZE or RTE_MIN_CACHE_LINE_SIZE would
> be clearer than RTE_CACHE_MIN_LINE_SIZE.

OK. I will resend the next version with RTE_CACHE_LINE_MIN_SIZE

> 
> >  /**
> >   * Force alignment to cache line.
> >   */
> >  #define __rte_cache_aligned __rte_aligned(RTE_CACHE_LINE_SIZE)
> >  
> > +/**
> > + * Force minimum cache line alignment.
> > + */
> > +#define __rte_cache_min_aligned __rte_aligned(RTE_CACHE_MIN_LINE_SIZE)
> 
> I'm not really convinced that __rte_cache_min_aligned is straightforward
> for someone reading the code that it means "aligned to the minimum cache
> line size supported by the dpdk".
> 
> In the two cases you are using this macro (mbuf structure and queue
> info), I'm wondering if using __attribute__((aligned(64))) wouldn't be
> clearer?
> - for mbuf, it could be a local define, like MBUF_ALIGN_SIZE
> - for queue info, using 64 makes sense as it's used to reserve space
>   for future use
> 
> What do you think?

IMO, it makes sense to keep "__rte_cache_min_aligned" as it will useful
for forcing the minimum alignment requirements in DPDK in future
structures.

Thoughts?

> 
> 
> Regards,
> Olivier