Re: [RFC 1/8] net/ena: fix warnings related to rte_memcpy and gcc-12

["Michał Krawczyk" <mk@semihalf.com>]

wt., 7 cze 2022 o 19:17 Stephen Hemminger <stephen@networkplumber.org>
napisał(a):
>
> Rte_memcpy is not needed for small objects only used on control
> path. Regular memcpy is as fast or faster and there is more
> robust since static analysis etc knows what it does.
>
> In this driver it was redefining all memcpy as rte_memcpy
> which is even worse.

Hi Stephen,

I would like to shed some light on why we're redefining all the memcpy
as rte_memcpy. The ENA HAL is unmodifiable, as it's shared across many
platforms and we cannot simply adjust it for the DPDK. We can use the
ena_plat_dpdk.h to change the ena_com (HAL) definitions, and that's
what we're doing with memcpy. It's being used on the data path for the
Tx, to copy the bounce buffers. Following the recommendations in [1]
plus the results from [2], we wanted to make use of the optimized
memcpy on the ENA's data path as well to reduce the CPU time spent in
the PMD. I'm worried that removing rte_memcpy from the ena_plat_dpdk.h
will result in some performance degradation for the ENA data path.
However I understand your concerns for the control path and I'm ok
with it.

[1] https://doc.dpdk.org/guides/prog_guide/writing_efficient_code.html#memory
[2] https://www.intel.com/content/www/us/en/developer/articles/technical/performance-optimization-of-memcpy-in-dpdk.html

Thanks,
Michal

>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  drivers/net/ena/base/ena_plat_dpdk.h | 10 +---------
>  drivers/net/ena/ena_ethdev.c         |  8 ++++----
>  drivers/net/ena/ena_rss.c            |  2 +-
>  3 files changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/ena/base/ena_plat_dpdk.h b/drivers/net/ena/base/ena_plat_dpdk.h
> index 8f2b3a87c2ab..caea763e3eca 100644
> --- a/drivers/net/ena/base/ena_plat_dpdk.h
> +++ b/drivers/net/ena/base/ena_plat_dpdk.h
> @@ -26,7 +26,6 @@
>  #include <rte_spinlock.h>
>
>  #include <sys/time.h>
> -#include <rte_memcpy.h>
>
>  typedef uint64_t u64;
>  typedef uint32_t u32;
> @@ -67,14 +66,7 @@ typedef uint64_t dma_addr_t;
>  #define ENA_UDELAY(x) rte_delay_us_block(x)
>
>  #define ENA_TOUCH(x) ((void)(x))
> -/* Redefine memcpy with caution: rte_memcpy can be simply aliased to memcpy, so
> - * make the redefinition only if it's safe (and beneficial) to do so.
> - */
> -#if defined(RTE_ARCH_X86) || defined(RTE_ARCH_ARM64_MEMCPY) || \
> -       defined(RTE_ARCH_ARM_NEON_MEMCPY)
> -#undef memcpy
> -#define memcpy rte_memcpy
> -#endif
> +
>  #define wmb rte_wmb
>  #define rmb rte_rmb
>  #define mb rte_mb
> diff --git a/drivers/net/ena/ena_ethdev.c b/drivers/net/ena/ena_ethdev.c
> index 68768cab7077..5f87429606e6 100644
> --- a/drivers/net/ena/ena_ethdev.c
> +++ b/drivers/net/ena/ena_ethdev.c
> @@ -481,7 +481,7 @@ ENA_PROXY_DESC(ena_com_get_dev_basic_stats, ENA_MP_DEV_STATS_GET,
>         ENA_TOUCH(rsp);
>         ENA_TOUCH(ena_dev);
>         if (stats != &adapter->basic_stats)
> -               rte_memcpy(stats, &adapter->basic_stats, sizeof(*stats));
> +               memcpy(stats, &adapter->basic_stats, sizeof(*stats));
>  }),
>         struct ena_com_dev *ena_dev, struct ena_admin_basic_stats *stats);
>
> @@ -496,7 +496,7 @@ ENA_PROXY_DESC(ena_com_get_eni_stats, ENA_MP_ENI_STATS_GET,
>         ENA_TOUCH(rsp);
>         ENA_TOUCH(ena_dev);
>         if (stats != (struct ena_admin_eni_stats *)&adapter->eni_stats)
> -               rte_memcpy(stats, &adapter->eni_stats, sizeof(*stats));
> +               memcpy(stats, &adapter->eni_stats, sizeof(*stats));
>  }),
>         struct ena_com_dev *ena_dev, struct ena_admin_eni_stats *stats);
>
> @@ -538,8 +538,8 @@ ENA_PROXY_DESC(ena_com_indirect_table_get, ENA_MP_IND_TBL_GET,
>         ENA_TOUCH(rsp);
>         ENA_TOUCH(ena_dev);
>         if (ind_tbl != adapter->indirect_table)
> -               rte_memcpy(ind_tbl, adapter->indirect_table,
> -                          sizeof(adapter->indirect_table));
> +               memcpy(ind_tbl, adapter->indirect_table,
> +                      sizeof(adapter->indirect_table));
>  }),
>         struct ena_com_dev *ena_dev, u32 *ind_tbl);
>
> diff --git a/drivers/net/ena/ena_rss.c b/drivers/net/ena/ena_rss.c
> index b6c4f76e3820..c723d3f5fca1 100644
> --- a/drivers/net/ena/ena_rss.c
> +++ b/drivers/net/ena/ena_rss.c
> @@ -59,7 +59,7 @@ void ena_rss_key_fill(void *key, size_t size)
>                 key_generated = true;
>         }
>
> -       rte_memcpy(key, default_key, size);
> +       memcpy(key, default_key, size);
>  }
>
>  int ena_rss_reta_update(struct rte_eth_dev *dev,
> --
> 2.35.1
>