Re: [dpdk-dev] [PATCH RFC v1 0/7] relax barriers for ENA PMD and small fixes

[Gavin Hu <Gavin.Hu@arm.com>]

Hi Igor,

> -----Original Message-----
> From: Chauskin, Igor <igorch@amazon.com>
> Sent: Monday, March 16, 2020 5:35 PM
> To: Gavin Hu <Gavin.Hu@arm.com>; dev@dpdk.org
> Cc: nd <nd@arm.com>; david.marchand@redhat.com; thomas@monjalon.net;
> mk@semihalf.com; Tzalik, Guy <gtzalik@amazon.com>; Schmeilin, Evgeny
> <evgenys@amazon.com>; mw@semihalf.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Phil Yang <Phil.Yang@arm.com>; Joyce Kong
> <Joyce.Kong@arm.com>; Bshara, Saeed <saeedb@amazon.com>;
> Matushevsky, Alexander <matua@amazon.com>
> Subject: RE: [PATCH RFC v1 0/7] relax barriers for ENA PMD and small fixes
> 
> Hi Gavin,
> 
> Thank you for the contribution.
> Please do not merge these changes (patches 0..7) till we (the ENA team)
> properly review and ack/nack.
> These changes can potentially provide performance improvement, yet we need
> to ensure they are applicable for all possible scenarios. Specifically, the
> behavior on x86 platforms is likely to be different.
> What testing have you done for these patches? Was x86 tested?
As noted in the cover letter, these patches were not tested as we don't have ENA NICs.
We rely on you to do that, any concerns and comments welcome. 
Yes, the behavior on x86 platforms is also different, Intel people are welcome to comment. 
/Gavin
> 
> Thanks,
> Igor
> 
> -----Original Message-----
> From: Gavin Hu <gavin.hu@arm.com>
> Sent: Friday, March 13, 2020 11:18 AM
> To: dev@dpdk.org
> Cc: nd@arm.com; david.marchand@redhat.com; thomas@monjalon.net;
> mk@semihalf.com; Tzalik, Guy <gtzalik@amazon.com>; Schmeilin, Evgeny
> <evgenys@amazon.com>; Chauskin, Igor <igorch@amazon.com>;
> mw@semihalf.com; Honnappa.Nagarahalli@arm.com;
> ruifeng.wang@arm.com; phil.yang@arm.com; joyce.kong@arm.com
> Subject: [EXTERNAL][PATCH RFC v1 0/7] relax barriers for ENA PMD and small
> fixes
> 
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> 
> 
> 
> To ensure the stores to the host memory are observed by NIC HW before a
> door bell ring to the NIC HW and the HW starts actions, for example, doing
> DMA, a barrier is required on weak memory ordering platforms, like aarch64.
> 
> However, unnecessarily too strong barriers like 'dsb' on aarch64 will dampen
> performance.
> 
> In a typical doorbell use case, as NIC and CPU are in the outer sharable domain,
> a lighter weight 'dmb osh' barrier is sufficient.
> 
> The patch set relaxes the barriers in similar places and include one more patch
> for statistics logging with relaxed ordering and the other patch removing
> duplicate memset.
> 
> Note this set is submitted for RFC as we don't have physical ENA NICs in the lab
> and the patch set was not verified nor benchmarked.
> 
> Gavin Hu (7):
>   net/ena: remove duplicate barrier
>   net/ena: relax the barrier for doorbell ring
>   net/ena: relax the rmb for DMA
>   net/ena: relax barrier for completion queue update
>   net/ena: relax the barrier for bounce buffer
>   net/ena: use c11 atomic for statistics
>   net/ena: remove duplicate memset
> 
>  drivers/net/ena/base/ena_eth_com.c   |  2 +-
>  drivers/net/ena/base/ena_eth_com.h   |  6 ++--
>  drivers/net/ena/base/ena_plat_dpdk.h |  2 +-
>  drivers/net/ena/ena_ethdev.c         | 46 +++++++++++++++++-----------
>  drivers/net/ena/ena_ethdev.h         |  8 ++---
>  5 files changed, 38 insertions(+), 26 deletions(-)
> 
> --
> 2.17.1