Re: [PATCH v3] ether: use a default for max Rx frame size in configure()

Hi Andriy,

I think this patch addressing just small issue in a bigger problem.
The way I see it all application needs to specify is the max packet size it expects to receive, nothing else(!). 
Currently we are forcing it to toggle multiple redundant fields. 

Wednesday, May 23, 2018 1:31 AM, Thomas Monjalon:

Subject: Re: [dpdk-dev] [PATCH v3] ether: use a default for max Rx frame

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IMO the changes are transparent for the PMDs (please see below), but
it might affect some applications. Here is the change in API behaviour:

Before the patch:
jumbo == 0, max_rx_pkt_len == 0, RESULT: max_rx_pkt_len =
ETHER_MAX_LEN jumbo == 0, max_rx_pkt_len == 10, RESULT:
max_rx_pkt_len = ETHER_MAX_LEN jumbo == 0, max_rx_pkt_len ==

1200,

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RESULT: max_rx_pkt_len = 1200 jumbo == 0, max_rx_pkt_len == 9K,
RESULT: max_rx_pkt_len = ETHER_MAX_LEN

jumbo == 1, max_rx_pkt_len == 0, RESULT: ERROR jumbo == 1,
max_rx_pkt_len == 10, RESULT: ERROR jumbo == 1, max_rx_pkt_len ==
1200, RESULT: max_rx_pkt_len = 1200 jumbo == 1, max_rx_pkt_len ==
9K, RESULT: ERROR or max_rx_pkt_len = 9K jumbo == 1, max_rx_pkt_len
== 90K, RESULT: ERROR


After the patch:
jumbo == 0, max_rx_pkt_len == 0, RESULT: max_rx_pkt_len =
ETHER_MAX_LEN jumbo == 0, max_rx_pkt_len == 10, RESULT: ERROR
(changed) jumbo == 0, max_rx_pkt_len == 1200, RESULT:

max_rx_pkt_len

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= 1200 jumbo == 0, max_rx_pkt_len == 9K, RESULT: ERROR (changed)

For example in the line above - the application wants to receive 9K frames. Why it is an error? Why forcing the application to set another redundant bit?
IMO The "jumbo_frame" bit can be set by the underlying PMD directly to the device registers given the max_rx_pkt_len configuration. 

Same apply to DEV_RX_OFFLOAD_SCATTER flag. Application doesn't need to set it. the PMD will choose the put multiple mbufs in Rx descriptor given the mbuf size and the max_rx_packet_len. 
API should be informative enough for the application to expect multi-segment packets on the receive. 

Finally the MTU. It is correct it stands for "max transmit unit" but it is threaded in the same way max_rx_pkt_len is (i.e. MTU sets the max packet len the port receives). 
We need to either clarify it only address transmit or remove it completely and maybe change max_rx_pkt_len name to mtu. 

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jumbo == 1, max_rx_pkt_len == 0, RESULT: max_rx_pkt_len = dev_info()
jumbo == 1, max_rx_pkt_len == 10, RESULT: ERROR jumbo == 1,
max_rx_pkt_len == 1200, RESULT: max_rx_pkt_len = 1200 jumbo == 1,
max_rx_pkt_len == 9K, RESULT: ERROR or max_rx_pkt_len = 9K jumbo

==

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1, max_rx_pkt_len == 90K, RESULT: ERROR

Only the apps which requested too small or too big normal frames
will be affected. In most cases it will be rather an error in the app...


Also I have looked through all the PMDs to confirm they are not
affected. Here is the summary:

af_packet
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = ETH_FRAME_LEN (1514)

ark
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = ETH_FRAME_LEN (16K - 128)

avp
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = avp->max_rx_pkt_len
rx_queue_setup() uses max_rx_pkt_len for scattering

bnx2x
configure() uses max_rx_pkt_len to set internal mtu
info() returns max_rx_pktlen = BNX2X_MAX_RX_PKT_LEN (15872)

bnxt
configure() uses max_rx_pkt_len to set internal mtu
info() returns max_rx_pktlen = BNXT_MAX_MTU + ETHER_HDR_LEN +
ETHER_CRC_LEN + VLAN_TAG_SIZE (9000 + 14 + 4 + 4)

bonding
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = internals->candidate_max_rx_pktlen or
ETHER_MAX_JUMBO_FRAME_LEN (0x3F00)

cxgbe
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = CXGBE_MAX_RX_PKTLEN (9000 + 14 + 4)
rx_queue_setup() checks max_rx_pkt_len boundaries

dpaa2
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = DPAA2_MAX_RX_PKT_LEN (10240)

e1000 (em)
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = em_get_max_pktlen() (0x2412, 0x1000,
1518, 0x3f00, depends on model)

e1000 (igb)
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = 0x3fff
start() writes max_rx_pkt_len to HW for jumbo frames only
start() uses max_rx_pkt_len for scattering

ena
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = adapter->max_mtu
start() checks max_rx_pkt_len boundaries

enic
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = enic->max_mtu + 14 + 4

fm10k
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = FM10K_MAX_PKT_SIZE (15 * 1024)
start() uses max_rx_pkt_len for scattering

i40e
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = I40E_FRAME_SIZE_MAX (9728)
rx_queue_config() checks max_rx_pkt_len boundaries

ixgbe
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = 15872 (9728 for vf)
start() writes max_rx_pkt_len to HW for jumbo frames only
start() uses max_rx_pkt_len for scattering

kni
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = UINT32_MAX

liquidio
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = LIO_MAX_RX_PKTLEN (64K)
start() checks max_rx_pkt_len boundaries

mlx4
configure() uses max_rx_pkt_len for scattering
info() returns max_rx_pktlen = 65536

mlx5
configure() uses max_rx_pkt_len for scattering
info() returns max_rx_pktlen = 65536

nfp
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = hw->mtu

null
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = (uint32_t)-1

pcap
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = (uint32_t)-1

qede
configure() uses max_rx_pkt_len for scattering + internal data
info() returns max_rx_pktlen = ETH_TX_MAX_NON_LSO_PKT_LEN (9700

- 4

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- 4
- 12 - 8)

ring
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = (uint32_t)-1

sfc
configure() uses max_rx_pkt_len to set internal data
info() returns max_rx_pktlen = EFX_MAC_PDU_MAX (9202 + 14 + 4 + 4 +
16)

szedata2
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = (uint32_t)-1

tap
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = ETHER_MAX_VLAN_FRAME_LEN (1518 +

4)

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thunderx
configure() uses max_rx_pkt_len for scattering + sets internal mtu
info() returns max_rx_pktlen = NIC_HW_MAX_FRS (9200)

vhost
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = (uint32_t)-1

virtio
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = VIRTIO_MAX_RX_PKTLEN (9728U)

vmxnet3
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = 16384;

xenvirt
configure() does not use max_rx_pkt_len
info() returns max_rx_pktlen = 2048


Regards,
Andriy