Re: [dpdk-dev] [PATCH v6 1/3] eal: introduce integer divide through reciprocal

[Pavan Nikhilesh Bhagavatula <pbhagavatula@caviumnetworks.com>]

On Wed, Sep 20, 2017 at 01:10:53PM +0000, Dumitrescu, Cristian wrote:
> Hi Pavan,
Hi Cristian,
>
> I think moving rte_reciprocal.[hc] to a common code area like EAL is a very good idea, so thanks for doing this work!
>
> One ask from my side: please do not change the existing code.
> 1. Keep the existing name for the 32-bit API functions and data structures (no _u32 name suffix), add the _u64 suffix just for the new API functions that you add.
> 	- If you want, you can create aliases with _32 name suffix for the existing 32-bit API
> 	- The only change to rte_sched.c should be header include line: #include "rte_reciprocal.h" -> #include <rte_reciprocal.h>
> 2. Do not do any cosmetic changes in existing code in rte_reciprocal.[hc] (such as adding CR+LF), as they result in lots of code churn for no real value
>
> Once these changes are done, the size of your patch set is reduced considerably.
>

Will do the changes once the licencing issues get sorted out(v7).

-Pavan

>
> > -----Original Message-----
> > From: Pavan Nikhilesh [mailto:pbhagavatula@caviumnetworks.com]
> > Sent: Wednesday, September 6, 2017 11:22 AM
> > To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>;
> > stephen@networkplumber.org
> > Cc: dev@dpdk.org; Pavan Bhagavatula
> > <pbhagavatula@caviumnetworks.com>
> > Subject: [dpdk-dev] [PATCH v6 1/3] eal: introduce integer divide through
> > reciprocal
> >
> > From: Pavan Bhagavatula <pbhagavatula@caviumnetworks.com>
> >
> > In some use cases of integer division, denominator remains constant and
> > numerator varies. It is possible to optimize division for such specific
> > scenarios.
> >
> > The librte_sched uses rte_reciprocal to optimize division so, moving it to
> > eal/common would allow other libraries and applications to use it.
> >
> > Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> > Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>
> > ---
> >
> > v6 changes:
> >  - remove cache alignment from rte_reciprocal_u{32/64}structures as they
> > would
> >  be embedded in other structures.
> >
> > v5 changes:
> >  - fix test print strings
> >
> > v4 changes:
> >  - minor fix for test cases
> >  - fix u32 divisor generation
> >
> > v3 changes:
> >  - fix x86_32 compilation issue
> >  - fix improper licence in test
> >
> > v2 changes:
> >  - fix compilation issues with .map files
> >  - add test cases for correctness and performance
> >  - remove extra licence inclusion
> >  - fix coding style issues
> >
> >  lib/librte_eal/bsdapp/eal/Makefile                               | 1 +
> >  lib/librte_eal/bsdapp/eal/rte_eal_version.map                    | 7 +++++++
> >  lib/librte_eal/common/Makefile                                   | 1 +
> >  lib/{librte_sched => librte_eal/common/include}/rte_reciprocal.h | 6 ++++--
> >  lib/{librte_sched => librte_eal/common}/rte_reciprocal.c         | 6 ++++--
> >  lib/librte_eal/linuxapp/eal/Makefile                             | 1 +
> >  lib/librte_eal/linuxapp/eal/rte_eal_version.map                  | 7 +++++++
> >  lib/librte_sched/Makefile                                        | 2 --
> >  lib/librte_sched/rte_sched.c                                     | 2 +-
> >  9 files changed, 26 insertions(+), 7 deletions(-)
> >  rename lib/{librte_sched => librte_eal/common/include}/rte_reciprocal.h
> > (87%)
> >  rename lib/{librte_sched => librte_eal/common}/rte_reciprocal.c (96%)
> >
> > diff --git a/lib/librte_eal/bsdapp/eal/Makefile
> > b/lib/librte_eal/bsdapp/eal/Makefile
> > index 005019e..56f9804 100644
> > --- a/lib/librte_eal/bsdapp/eal/Makefile
> > +++ b/lib/librte_eal/bsdapp/eal/Makefile
> > @@ -88,6 +88,7 @@ SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) +=
> > malloc_elem.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) += malloc_heap.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) += rte_keepalive.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) += rte_service.c
> > +SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) += rte_reciprocal.c
> >
> >  # from arch dir
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_BSDAPP) += rte_cpuflags.c
> > diff --git a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > index aac6fd7..90d7258 100644
> > --- a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > +++ b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > @@ -237,3 +237,10 @@ EXPERIMENTAL {
> >  	rte_service_unregister;
> >
> >  } DPDK_17.08;
> > +
> > +DPDK_17.11 {
> > +	global:
> > +
> > +	rte_reciprocal_value;
> > +
> > +} DPDK_17.08;
> > diff --git a/lib/librte_eal/common/Makefile
> > b/lib/librte_eal/common/Makefile
> > index e8fd67a..a680b2d 100644
> > --- a/lib/librte_eal/common/Makefile
> > +++ b/lib/librte_eal/common/Makefile
> > @@ -42,6 +42,7 @@ INC += rte_hexdump.h rte_devargs.h rte_bus.h
> > rte_dev.h rte_vdev.h
> >  INC += rte_pci_dev_feature_defs.h rte_pci_dev_features.h
> >  INC += rte_malloc.h rte_keepalive.h rte_time.h
> >  INC += rte_service.h rte_service_component.h
> > +INC += rte_reciprocal.h
> >
> >  GENERIC_INC := rte_atomic.h rte_byteorder.h rte_cycles.h rte_prefetch.h
> >  GENERIC_INC += rte_spinlock.h rte_memcpy.h rte_cpuflags.h rte_rwlock.h
> > diff --git a/lib/librte_sched/rte_reciprocal.h
> > b/lib/librte_eal/common/include/rte_reciprocal.h
> > similarity index 87%
> > rename from lib/librte_sched/rte_reciprocal.h
> > rename to lib/librte_eal/common/include/rte_reciprocal.h
> > index 5e21f09..b6d752f 100644
> > --- a/lib/librte_sched/rte_reciprocal.h
> > +++ b/lib/librte_eal/common/include/rte_reciprocal.h
> > @@ -29,13 +29,15 @@ struct rte_reciprocal {
> >  	uint8_t sh1, sh2;
> >  };
> >
> > -static inline uint32_t rte_reciprocal_divide(uint32_t a, struct rte_reciprocal
> > R)
> > +static inline uint32_t
> > +rte_reciprocal_divide(uint32_t a, struct rte_reciprocal R)
> >  {
> >  	uint32_t t = (uint32_t)(((uint64_t)a * R.m) >> 32);
> >
> >  	return (t + ((a - t) >> R.sh1)) >> R.sh2;
> >  }
> >
> > -struct rte_reciprocal rte_reciprocal_value(uint32_t d);
> > +struct rte_reciprocal
> > +rte_reciprocal_value(uint32_t d);
> >
>
> Please remove these cosmetic changes that result in code churn for no real value.
>
> >  #endif /* _RTE_RECIPROCAL_H_ */
> > diff --git a/lib/librte_sched/rte_reciprocal.c
> > b/lib/librte_eal/common/rte_reciprocal.c
> > similarity index 96%
> > rename from lib/librte_sched/rte_reciprocal.c
> > rename to lib/librte_eal/common/rte_reciprocal.c
> > index 652f023..7ab99b4 100644
> > --- a/lib/librte_sched/rte_reciprocal.c
> > +++ b/lib/librte_eal/common/rte_reciprocal.c
> > @@ -41,7 +41,8 @@
> >  /* find largest set bit.
> >   * portable and slow but does not matter for this usage.
> >   */
> > -static inline int fls(uint32_t x)
> > +static inline int
> > +fls(uint32_t x)
> >  {
> >  	int b;
> >
> > @@ -53,7 +54,8 @@ static inline int fls(uint32_t x)
> >  	return 0;
> >  }
> >
> > -struct rte_reciprocal rte_reciprocal_value(uint32_t d)
> > +struct rte_reciprocal
> > +rte_reciprocal_value(uint32_t d)
> >  {
> >  	struct rte_reciprocal R;
> >  	uint64_t m;
>
> Please remove these cosmetic changes that result in code churn for no real value.
>
> > diff --git a/lib/librte_eal/linuxapp/eal/Makefile
> > b/lib/librte_eal/linuxapp/eal/Makefile
> > index 90bca4d..98f3b8e 100644
> > --- a/lib/librte_eal/linuxapp/eal/Makefile
> > +++ b/lib/librte_eal/linuxapp/eal/Makefile
> > @@ -100,6 +100,7 @@ SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) +=
> > malloc_elem.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) += malloc_heap.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) += rte_keepalive.c
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) += rte_service.c
> > +SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) += rte_reciprocal.c
> >
> >  # from arch dir
> >  SRCS-$(CONFIG_RTE_EXEC_ENV_LINUXAPP) += rte_cpuflags.c
> > diff --git a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > index 3a8f154..2070cba 100644
> > --- a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > +++ b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > @@ -242,3 +242,10 @@ EXPERIMENTAL {
> >  	rte_service_unregister;
> >
> >  } DPDK_17.08;
> > +
> > +DPDK_17.11 {
> > +	global:
> > +
> > +	rte_reciprocal_value;
> > +
> > +} DPDK_17.08;
> > diff --git a/lib/librte_sched/Makefile b/lib/librte_sched/Makefile
> > index 18274e7..569656b 100644
> > --- a/lib/librte_sched/Makefile
> > +++ b/lib/librte_sched/Makefile
> > @@ -52,10 +52,8 @@ LIBABIVER := 1
> >  # all source are stored in SRCS-y
> >  #
> >  SRCS-$(CONFIG_RTE_LIBRTE_SCHED) += rte_sched.c rte_red.c rte_approx.c
> > -SRCS-$(CONFIG_RTE_LIBRTE_SCHED) += rte_reciprocal.c
> >
> >  # install includes
> >  SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include := rte_sched.h
> > rte_bitmap.h rte_sched_common.h rte_red.h rte_approx.h
> > -SYMLINK-$(CONFIG_RTE_LIBRTE_SCHED)-include += rte_reciprocal.h
> >
> >  include $(RTE_SDK)/mk/rte.lib.mk
> > diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
> > index b7cba11..3b8ccaa 100644
> > --- a/lib/librte_sched/rte_sched.c
> > +++ b/lib/librte_sched/rte_sched.c
> > @@ -42,12 +42,12 @@
> >  #include <rte_prefetch.h>
> >  #include <rte_branch_prediction.h>
> >  #include <rte_mbuf.h>
> > +#include <rte_reciprocal.h>
> >
> >  #include "rte_sched.h"
> >  #include "rte_bitmap.h"
> >  #include "rte_sched_common.h"
> >  #include "rte_approx.h"
> > -#include "rte_reciprocal.h"
> >
> >  #ifdef __INTEL_COMPILER
> >  #pragma warning(disable:2259) /* conversion may lose significant bits */
> > --
> > 2.7.4
>
> Regards,
> Cristian
>