Re: [dpdk-dev] [PATCH v1 01/14] ring: remove split cacheline build setting

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

On Tue, Feb 28, 2017 at 11:57:03AM +0000, Bruce Richardson wrote:
> On Tue, Feb 28, 2017 at 05:05:13PM +0530, Jerin Jacob wrote:
> > On Thu, Feb 23, 2017 at 05:23:54PM +0000, Bruce Richardson wrote:
> > > Users compiling DPDK should not need to know or care about the arrangement
> > > of cachelines in the rte_ring structure. Therefore just remove the build
> > > option and set the structures to be always split. For improved
> > > performance use 128B rather than 64B alignment since it stops the producer
> > > and consumer data being on adjacent cachelines.
> > > 
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >  config/common_base                     | 1 -
> > >  doc/guides/rel_notes/release_17_05.rst | 6 ++++++
> > >  lib/librte_ring/rte_ring.c             | 2 --
> > >  lib/librte_ring/rte_ring.h             | 8 ++------
> > >  4 files changed, 8 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/config/common_base b/config/common_base
> > > index aeee13e..099ffda 100644
> > > --- a/config/common_base
> > > +++ b/config/common_base
> > > @@ -448,7 +448,6 @@ CONFIG_RTE_LIBRTE_PMD_NULL_CRYPTO=y
> > >  #
> > >  CONFIG_RTE_LIBRTE_RING=y
> > >  CONFIG_RTE_LIBRTE_RING_DEBUG=n
> > > -CONFIG_RTE_RING_SPLIT_PROD_CONS=n
> > >  CONFIG_RTE_RING_PAUSE_REP_COUNT=0
> > >  
> > >  #
> > > diff --git a/doc/guides/rel_notes/release_17_05.rst b/doc/guides/rel_notes/release_17_05.rst
> > > index e25ea9f..ea45e0c 100644
> > > --- a/doc/guides/rel_notes/release_17_05.rst
> > > +++ b/doc/guides/rel_notes/release_17_05.rst
> > > @@ -110,6 +110,12 @@ API Changes
> > >     Also, make sure to start the actual text at the margin.
> > >     =========================================================
> > >  
> > > +* **Reworked rte_ring library**
> > > +
> > > +  The rte_ring library has been reworked and updated. The following changes
> > > +  have been made to it:
> > > +
> > > +  * removed the build-time setting ``CONFIG_RTE_RING_SPLIT_PROD_CONS``
> > >  
> > >  ABI Changes
> > >  -----------
> > > diff --git a/lib/librte_ring/rte_ring.c b/lib/librte_ring/rte_ring.c
> > > index ca0a108..4bc6da1 100644
> > > --- a/lib/librte_ring/rte_ring.c
> > > +++ b/lib/librte_ring/rte_ring.c
> > > @@ -127,10 +127,8 @@ rte_ring_init(struct rte_ring *r, const char *name, unsigned count,
> > >  	/* compilation-time checks */
> > >  	RTE_BUILD_BUG_ON((sizeof(struct rte_ring) &
> > >  			  RTE_CACHE_LINE_MASK) != 0);
> > > -#ifdef RTE_RING_SPLIT_PROD_CONS
> > >  	RTE_BUILD_BUG_ON((offsetof(struct rte_ring, cons) &
> > >  			  RTE_CACHE_LINE_MASK) != 0);
> > > -#endif
> > >  	RTE_BUILD_BUG_ON((offsetof(struct rte_ring, prod) &
> > >  			  RTE_CACHE_LINE_MASK) != 0);
> > >  #ifdef RTE_LIBRTE_RING_DEBUG
> > > diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
> > > index 72ccca5..04fe667 100644
> > > --- a/lib/librte_ring/rte_ring.h
> > > +++ b/lib/librte_ring/rte_ring.h
> > > @@ -168,7 +168,7 @@ struct rte_ring {
> > >  		uint32_t mask;           /**< Mask (size-1) of ring. */
> > >  		volatile uint32_t head;  /**< Producer head. */
> > >  		volatile uint32_t tail;  /**< Producer tail. */
> > > -	} prod __rte_cache_aligned;
> > > +	} prod __rte_aligned(RTE_CACHE_LINE_SIZE * 2);
> > 
> > I think we need to use RTE_CACHE_LINE_MIN_SIZE instead of
> > RTE_CACHE_LINE_SIZE for alignment here. PPC and ThunderX1 targets are cache line
> > size of 128B
> > 
> Sure.
> 
> However, can you perhaps try a performance test and check to see if
> there is a performance difference between the two values before I change
> it? In my tests I see improved performance by having an extra blank
> cache-line between the producer and consumer data.

Sure. Which test are you running to measure the performance difference?
Is it app/test/test_ring_perf.c?

> 
> /Bruce