> -----Original Message----- > From: Andrew Rybchenko <arybche...@solarflare.com> > Sent: Sunday, August 18, 2019 10:01 AM > To: Shahaf Shuler <shah...@mellanox.com>; pbhagavat...@marvell.com; > jer...@marvell.com; ferruh.yi...@intel.com; John McNamara > <john.mcnam...@intel.com>; Marko Kovacevic > <marko.kovace...@intel.com>; Thomas Monjalon <tho...@monjalon.net> > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH 2/7] ethdev: add mbuf RSS update as a > offload > > On 8/18/19 9:18 AM, Shahaf Shuler wrote: > > Sunday, August 18, 2019 8:39 AM, Andrew Rybchenko: > >> <marko.kovace...@intel.com>; Thomas Monjalon > <tho...@monjalon.net> > >> Cc: dev@dpdk.org > >> Subject: Re: [dpdk-dev] [PATCH 2/7] ethdev: add mbuf RSS update as a > >> offload > >> > >> On 8/18/19 7:52 AM, Shahaf Shuler wrote: > >>> Friday, August 16, 2019 10:48 AM, Andrew Rybchenko: > >>>> Subject: Re: [dpdk-dev] [PATCH 2/7] ethdev: add mbuf RSS update as > >>>> a offload > >>>> > >>>> On 8/16/19 8:55 AM, pbhagavat...@marvell.com wrote: > >>>>> From: Pavan Nikhilesh <pbhagavat...@marvell.com> > >>>>> > >>>>> Add new Rx offload flag `DEV_RX_OFFLOAD_RSS_HASH` which can be > >> used > >>>> to > >>>>> enable/disable PMDs write to `rte_mbuf::hash::rss`. > >>>> It should be highlighted that presence of the RSS hash is indicated > >>>> by PKT_RX_RSS_HASH flag in mbuf anyway. Now applications have a > way > >>>> to check that RSS hash delivery is supported and should enable the > >>>> offload if RSS hash is used. PMD may still provide the hash even if > >>>> the offload is not enabled. > >>> I don't understand how PMDs should act w/ this addition when > >>> considering > >> the API breakage to application. > >> > >> There is a deprecation notice for it. > >> I mentioned in my review notes for one of patches in the series that > >> the change should be highlighted in release notes. > >> Yes, it is absolutely required if these patches are accepted. > >> > >>> Currently application don't set this flag, and expect to get the RSS > >>> hash > >> result on mbuf. > >>> If PMDs will not set the RSS hash result when flag is not present > >>> then > >> applications might break. > >>> If they will always set, then there is no meaning for it. > >>> > >>> as I understand the motivation to save few cycles on the PMD receive > >>> path, > >> if we want to include it we should treat it as API breakage and > >> documents it on the release notes. > >>> My option is that some offload should just be usable (OOB) by the > >>> fact user > >> enabled them (e.g. RSS). no need to complicate the user by checking > >> and set this field. > >> > >> What I don't understand is why some offloads should just work but > >> another requires action to enable it. Just because it is the current > >> state of things - I don't think it is a good motivation. Sorry. > > Not because it is the current state of things, because it makes user > experience much simpler. > > If so, it would be simpler to have no controls at all and always have > everything possible. > > > You enabled RSS -> you get full RSS behavior > > You enable distribution across many queues here. > RSS hash availability is a side effect here.
I disagree. There is at least one RSS spec (Microsoft NDIS) that define it part of the RSS action. [1] Bottom of page " The NIC always passes on the 32-bit hash value." Am not spec pedantic, just to emphasize that natively drivers expects to have the RSS hash on the packet descriptor. As for the rest - I think you spread the two different approach correctly. [1] https://docs.microsoft.com/en-us/windows-hardware/drivers/network/introduction-to-receive-side-scaling > > > You set a flow rule w/ mark -> you get full flow mark behavior You set > > checksum -> you get full csum behavior. > > > >> I think more applications use checksum offloads than RSS hash, but it > >> is still required to enable it. It looks like no single DPDK example > >> uses RSS hash. So, I guess it not widely used by applications as well. > > Well there is at least one called ovs-dpdk, that use the RSS result as the > > key > to access the EMC. > > I know of few more, not upstream, ones. > > > >> Anyway these 2 patches for flow action and RSS hash make all Rx > >> offloads consistent - if you need something, enable it. > > But the user enabled it - > > It enabled RSS by setting ETH_MQ_RX_RSS, why does it need to enable > another flag? > > Answered above. If you need distribution it does not mean that you need > RSS hash information. There are really many examples when you don't really > need it. > > > Same for flow mark. > > > >> And the question is not to save few cycles in the PMD receive path. > >> It makes is possible to not deliver both from NIC to host. > >> 8 bytes (4 RSS hash and 4 flow mark) are more than 10% for the > >> smallest packets. > > There is always the line between how much tight control we want to > provide to user (to save cycles/ to save PCI BW) and how much it will be > simple for the user to work on top. > > My opinion is that we need to have some basics. > > Many thanks, your arguments make sense. I vote for consistency and more > fine grained control which allows more optimizations and allow to squeeze > more performance from HW and SW. So, my line is a bit lower. I don't think > that these two patches make user control over-complicated. > > >>>>> Signed-off-by: Pavan Nikhilesh <pbhagavat...@marvell.com> > >>>> Reviewed-by: Andrew Rybchenko <arybche...@solarflare.com> > >>>> > >>>> with above and one note below fixed. > >>>> > >>>>> --- > >>>>> doc/guides/nics/features.rst | 2 ++ > >>>>> lib/librte_ethdev/rte_ethdev.h | 1 + > >>>>> 2 files changed, 3 insertions(+) > >>>>> > >>>>> diff --git a/doc/guides/nics/features.rst > >>>>> b/doc/guides/nics/features.rst index d4d55f721..f79b69b38 100644 > >>>>> --- a/doc/guides/nics/features.rst > >>>>> +++ b/doc/guides/nics/features.rst > >>>>> @@ -274,6 +274,7 @@ Supports RSS hashing on RX. > >>>>> > >>>>> * **[uses] user config**: ``dev_conf.rxmode.mq_mode`` = > >>>> ``ETH_MQ_RX_RSS_FLAG``. > >>>>> * **[uses] user config**: ``dev_conf.rx_adv_conf.rss_conf``. > >>>>> +* **[uses] rte_eth_rxconf,rte_eth_rxmode**: > >>>> ``offloads:DEV_RX_OFFLOAD_RSS_HASH``. > >>>>> * **[provides] rte_eth_dev_info**: ``flow_type_rss_offloads``. > >>>>> * **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_RSS_HASH``, > >> ``mbuf.rss``. > >>>>> @@ -286,6 +287,7 @@ Inner RSS > >>>>> Supports RX RSS hashing on Inner headers. > >>>>> > >>>>> * **[uses] rte_flow_action_rss**: ``level``. > >>>>> +* **[uses] rte_eth_rxconf,rte_eth_rxmode**: > >>>> ``offloads:DEV_RX_OFFLOAD_RSS_HASH``. > >>>>> * **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_RSS_HASH``, > >> ``mbuf.rss``. > >>>>> > >>>>> diff --git a/lib/librte_ethdev/rte_ethdev.h > >>>>> b/lib/librte_ethdev/rte_ethdev.h index f97f0a6e5..889486a11 100644 > >>>>> --- a/lib/librte_ethdev/rte_ethdev.h > >>>>> +++ b/lib/librte_ethdev/rte_ethdev.h > >>>>> @@ -1013,6 +1013,7 @@ struct rte_eth_conf { > >>>>> #define DEV_RX_OFFLOAD_KEEP_CRC 0x00010000 > >>>>> #define DEV_RX_OFFLOAD_SCTP_CKSUM 0x00020000 > >>>>> #define DEV_RX_OFFLOAD_OUTER_UDP_CKSUM 0x00040000 > >>>>> +#define DEV_RX_OFFLOAD_RSS_HASH 0x00080000 > >>>> Should be added to rte_rx_offload_names in > >>>> lib/librte_ethdev/rte_ethdev.c.
