netdev - Re: [PATCH v2 net-next 2/4] vmxnet3: add support to get/set rx flow hash

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Message-ID: <EE27E96B-155D-445E-B205-861B7D516BE1@vmware.com>
Date:   Thu, 28 May 2020 19:29:34 +0000
From:   Ronak Doshi <doshir@...are.com>
To:     Michal Kubecek <mkubecek@...e.cz>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Pv-drivers <Pv-drivers@...are.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 2/4] vmxnet3: add support to get/set rx flow
 hash


On 5/28/20, 12:21 PM, "Michal Kubecek" <mkubecek@...e.cz> wrote:

>    On Thu, May 28, 2020 at 11:36:13AM -0700, Ronak Doshi wrote:
>    > With vmxnet3 version 4, the emulation supports multiqueue(RSS) for
>    > UDP and ESP traffic. A guest can enable/disable RSS for UDP/ESP over
>    > IPv4/IPv6 by issuing commands introduced in this patch. ESP ipv6 is
>    > not yet supported in this patch.
>    > 
>    > This patch implements get_rss_hash_opts and set_rss_hash_opts
>    > methods to allow querying and configuring different Rx flow hash
>    > configurations.
>    > 
>    > Signed-off-by: Ronak Doshi <doshir@...are.com>
>    > ---
>
>    This still suffers from the inconsistency between get and set handler
>   I already pointed out in v1:
>   
>    - there is no way to change VMXNET3_RSS_FIELDS_TCPIP{4,6} bits
>    - get_rxnfc() may return value that set_rxnfc() won't accept
>    - get_rxnfc() may return different value than set_rxnfc() set
>    
>    Above, vmxnet3_get_rss_hash_opts() returns 0 or
>    RXH_L4_B_0_1 | RXH_L4_B_2_3 | RXH_IP_SRC | RXH_IP_DST for any of
>    {TCP,UDP}_V{4,6}_FLOW, depending on corresponding bit in rss_fields. But
>    here you accept only all four bits for TCP (both v4 and v6) and either
>    the two RXH_IP_* bits or all four for UDP.
>    
>    Michal
 
Hi Michal,

That is intentional as vmxnet3 device always expects TCP rss to be enabled
if rss is supported. If RSS is enabled, by default rss_fields has TCP/IP RSS
supported and cannot be disabled. Its only for UDP/ESP flows the config
can change. Hence, get_rss always reports TCP/IP RSS enabled, and set_rss
does not accept disabling TCP RSS. Hope this answers your concern.

Thanks,
Ronak