[ovs-dev] [PATCH v6] Configurable Link State Change (LSC) detection mode
Jan Scheurich
jan.scheurich at ericsson.com
Tue Mar 27 14:09:39 UTC 2018
Hi Ilya,
This patch is the upstream version of a fix we implemented downstream a year ago to fix the issue with massive packet drop of OVS-DPDK on Fortville NICs.
The root cause of this packet drop was the extended blocking of the ovs-vswitchd by the i40e PMD during the rte_eth_link_get_nowait() function, which caused the PMDs to hang for up to 40ms during upcalls.
At the time switching to LSC interrupt was the only viable solution. OVS still polls the links state from DPDK with rte_eth_link_get_nowait() but DPDK returns the locally buffered link state, updated through LSC interrupt, instead of going through the FVL's admin queue.
Now, the new i40e PMD fix in DPDK bypassing the admin queue should also solve the problem with Fortville NICs. It would have to be backported to older DPDK releases to be useful as fix for OVS 2.6, 2.7, 2.8 and 2.9, whereas the LSC interrupt solution in OVS would work as back-port for all OVS versions since 2.6.
That's why we still think there is value in pursuing the LSC interrupt track.
BR, Jan
> -----Original Message-----
> From: ovs-dev-bounces at openvswitch.org [mailto:ovs-dev-bounces at openvswitch.org] On Behalf Of Ilya Maximets
> Sent: Tuesday, 27 March, 2018 13:17
> To: Stokes, Ian <ian.stokes at intel.com>; Róbert Mulik <robert.mulik at ericsson.com>; dev at openvswitch.org
> Subject: Re: [ovs-dev] [PATCH v6] Configurable Link State Change (LSC) detection mode
>
> On 27.03.2018 13:19, Stokes, Ian wrote:
> >> It is possible to change LSC detection mode to polling or interrupt mode
> >> for DPDK interfaces. The default is polling mode. To set interrupt mode,
> >> option dpdk-lsc-interrupt has to be set to true.
> >>
> >> In polling mode more processor time is needed, since the OVS repeatedly
> >> reads the link state with a short period. It can lead to packet loss for
> >> certain systems.
> >>
> >> In interrupt mode the hardware itself triggers an interrupt when link
> >> state change happens, so less processing time needs for the OVS.
> >>
> >> For detailed description and usage see the dpdk install documentation.
>
> Could you, please, better describe why we need this change?
> Because we're not removing the polling thread. OVS will still
> poll the link states periodically. This config option has
> no effect on that side. Also, link state polling in OVS uses
> 'rte_eth_link_get_nowait()' function which will be called in both
> cases and should not wait for hardware reply in any implementation.
>
> There was recent bug fix for intel NICs that fixes waiting of an
> admin queue on link state requests despite of 'no_wait' flag:
> http://dpdk.org/ml/archives/dev/2018-March/092156.html
> Will this fix your target case?
>
> So, the difference of execution time of 'rte_eth_link_get_nowait()'
> with enabled and disabled interrupts should be not so significant.
> Do you have performance measurements? Measurement with above fix applied?
>
>
> >
> > Thanks for working on this Robert.
> >
> > I've completed some testing including the case where LSC is not supported, in which case the port will remain in a down state and
> fail rx/tx traffic. This behavior conforms to the netdev_reconfigure expectations in the fail case so that's ok.
>
> I'm not sure if this is acceptable. For example, we're not failing
> reconfiguration in case of issues with number of queues. We're trying
> different numbers until we have working configuration.
> Maybe we need the same fall-back mechanism in case of not supported LSC
> interrupts? (MTU setup errors are really uncommon unlike LSC interrupts'
> support in PMDs).
>
> >
> > I'm a bit late to the thread but I have a few other comments below.
> >
> > I'd like to get this patch in the next pull request if possible so I'd appreciate if others can give any comments on the patch also.
> >
> > Thanks
> > Ian
> >
> >>
> >> Signed-off-by: Robert Mulik <robert.mulik at ericsson.com>
> >> ---
> >> v5 -> v6:
> >> - DPDK install documentation updated.
> >> - Status of lsc_interrupt_mode of DPDK interfaces can be read by command
> >> ovs-appctl dpif/show.
> >> - It was suggested to check if the HW supports interrupt mode, but it is
> >> not
> >> possible to do without DPDK code change, so it is skipped from this
> >> patch.
> >> ---
> >> Documentation/intro/install/dpdk.rst | 33
> >> +++++++++++++++++++++++++++++++++
> >> lib/netdev-dpdk.c | 24 ++++++++++++++++++++++--
> >> vswitchd/vswitch.xml | 17 +++++++++++++++++
> >> 3 files changed, 72 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/Documentation/intro/install/dpdk.rst
> >> b/Documentation/intro/install/dpdk.rst
> >> index ed358d5..eb1bc7b 100644
> >> --- a/Documentation/intro/install/dpdk.rst
> >> +++ b/Documentation/intro/install/dpdk.rst
> >> @@ -628,6 +628,39 @@ The average number of packets per output batch can be
> >> checked in PMD stats::
> >>
> >> $ ovs-appctl dpif-netdev/pmd-stats-show
> >>
> >> +Link State Change (LSC) detection configuration
> >> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> +
> >> +There are two methods to get the information when Link State Change
> >> +(LSC) happens on a network interface: by polling or interrupt.
> >> +
> >> +With the polling method, the main process checks the link state on a
> >> +fixed interval. This fixed interval determines how fast a link change
> >> +is detected.
> >> +
> >> +If interrupts are used to get LSC information, the hardware itself
> >> +triggers an interrupt when link state change happens, the interrupt
> >> +thread wakes up from sleep, updates the information, and goes back to
> >> +sleep mode. When no link state change happens (most of the time), the
> >> +thread remains in sleep mode and doesn`t use processor time at all. The
> >> +disadvantage of this method is that when an interrupt happens, the
> >> +processor has to handle it immediately, so it puts the currently
> >> +running process to background, handles the interrupt, and takes the
> >> background process back.
> >> +
> >> +Note that not all PMD drivers support LSC interrupts.
> >> +
> >> +The default configuration is polling mode. To set interrupt mode,
> >> +option ``dpdk-lsc-interrupt`` has to be set to ``true``.
> >> +
> >> +Command to set interrupt mode for a specific interface::
> >> + $ ovs-vsctl set interface <iface_name>
> >> +options:dpdk-lsc-interrupt=true
> >> +
> >> +Command to set polling mode for a specific interface::
> >> + $ ovs-vsctl set interface <iface_name>
> >> +options:dpdk-lsc-interrupt=false
> >> +
> >> +Command to remove ``dpdk-lsc-interrupt`` option::
> >> + $ ovs-vsctl remove interface <iface_name> options
> >> +dpdk-lsc-interrupt
> >
> > Just a query, why do we need the above option to remove lsc, is setting lsc true or false with the previous commands not enough?
> >
> >> +
> >> Limitations
> >> ------------
> >>
> >> diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c index 94fb163..e2794e8
> >> 100644
> >> --- a/lib/netdev-dpdk.c
> >> +++ b/lib/netdev-dpdk.c
> >> @@ -433,6 +433,12 @@ struct netdev_dpdk {
> >> /* DPDK-ETH hardware offload features,
> >> * from the enum set 'dpdk_hw_ol_features' */
> >> uint32_t hw_ol_features;
> >> +
> >> + /* Properties for link state change detection mode.
> >> + * If lsc_interrupt_mode is set to false, poll mode is used,
> >> + * otherwise interrupt mode is used. */
> >> + bool requested_lsc_interrupt_mode;
> >> + bool lsc_interrupt_mode;
> >> );
> >>
> >> PADDED_MEMBERS(CACHE_LINE_SIZE,
> >> @@ -686,12 +692,14 @@ dpdk_watchdog(void *dummy OVS_UNUSED) }
> >>
> >> static int
> >> -dpdk_eth_dev_queue_setup(struct netdev_dpdk *dev, int n_rxq, int n_txq)
> >> +dpdk_eth_dev_port_config(struct netdev_dpdk *dev, int n_rxq, int n_txq)
> >> {
> >> int diag = 0;
> >> int i;
> >> struct rte_eth_conf conf = port_conf;
> >>
> >> + conf.intr_conf.lsc = dev->lsc_interrupt_mode;
> >
> > Should above be dev->requested_lsc_interrupt_mode? Similar to how we request MTUs, we first have to validate if it's supported.
> > Since we have no way of knowing if the interrupt mode is supported at the moment we should set conf.intr_conf.lsc = dev-
> >requested_lsc_interrupt_mode and once configuration succeeds set dev->lsc_interrupt_mode = conf.intr_conf.lsc.
> >
> > If we don't then I'm not sure of the purpose of having requested_lsc_interrupt_mode and a separate lsc_interrupt_mode for dev.
> >
> > Thoughts?
> >
> >> +
> >> /* For some NICs (e.g. Niantic), scatter_rx mode needs to be
> >> explicitly
> >> * enabled. */
> >> if (dev->mtu > ETHER_MTU) {
> >> @@ -801,7 +809,7 @@ dpdk_eth_dev_init(struct netdev_dpdk *dev)
> >> n_rxq = MIN(info.max_rx_queues, dev->up.n_rxq);
> >> n_txq = MIN(info.max_tx_queues, dev->up.n_txq);
> >>
> >> - diag = dpdk_eth_dev_queue_setup(dev, n_rxq, n_txq);
> >> + diag = dpdk_eth_dev_port_config(dev, n_rxq, n_txq);
> >> if (diag) {
> >> VLOG_ERR("Interface %s(rxq:%d txq:%d) configure error: %s",
> >> dev->up.name, n_rxq, n_txq, rte_strerror(-diag));
> >
> > With the change from dpdk_eth_dev_queue_setup to dpdk_eth_dev_port_config I think we need to improve the error message
> also logged above.
> > Instead of only reporting the rxq and txq we should include the requested lsc mode also as that could cause a failure if not
> supported.
> >
> > @@ -
> >> 897,6 +905,7 @@ common_construct(struct netdev *netdev, dpdk_port_t
> >> port_no,
> >> dev->flags = 0;
> >> dev->requested_mtu = ETHER_MTU;
> >> dev->max_packet_len = MTU_TO_FRAME_LEN(dev->mtu);
> >> + dev->requested_lsc_interrupt_mode = 0;
> >> ovsrcu_index_init(&dev->vid, -1);
> >> dev->vhost_reconfigured = false;
> >> dev->attached = false;
> >> @@ -1320,6 +1329,8 @@ netdev_dpdk_get_config(const struct netdev *netdev,
> >> struct smap *args)
> >> } else {
> >> smap_add(args, "rx_csum_offload", "false");
> >> }
> >> + smap_add(args, "lsc_interrupt_mode",
> >> + dev->lsc_interrupt_mode?"true":"false");
> >
> > Need space before/after operators '?' and ':' above.
> >
> >> }
> >> ovs_mutex_unlock(&dev->mutex);
> >>
> >> @@ -1520,6 +1531,12 @@ netdev_dpdk_set_config(struct netdev *netdev, const
> >> struct smap *args,
> >> goto out;
> >> }
> >>
> >> + bool lsc_interrupt_mode = smap_get_bool(args, "dpdk-lsc-interrupt",
> >
> > This comes down to style preference but can you declare this bool at the beginning of the function? There are other bool variable in
> the function declared there already so it keeps with the existing style of the function.
>
> +1
>
> >
> >> false);
> >> + if (dev->requested_lsc_interrupt_mode != lsc_interrupt_mode) {
> >> + dev->requested_lsc_interrupt_mode = lsc_interrupt_mode;
> >> + netdev_request_reconfigure(netdev);
> >> + }
> >> +
> >> rx_fc_en = smap_get_bool(args, "rx-flow-ctrl", false);
> >> tx_fc_en = smap_get_bool(args, "tx-flow-ctrl", false);
> >> autoneg = smap_get_bool(args, "flow-ctrl-autoneg", false); @@ -3546,6
> >> +3563,7 @@ netdev_dpdk_reconfigure(struct netdev *netdev)
> >> if (netdev->n_txq == dev->requested_n_txq
> >> && netdev->n_rxq == dev->requested_n_rxq
> >> && dev->mtu == dev->requested_mtu
> >> + && dev->lsc_interrupt_mode == dev->requested_lsc_interrupt_mode
> >> && dev->rxq_size == dev->requested_rxq_size
> >> && dev->txq_size == dev->requested_txq_size
> >> && dev->socket_id == dev->requested_socket_id) { @@ -3561,6
> >> +3579,8 @@ netdev_dpdk_reconfigure(struct netdev *netdev)
> >> goto out;
> >> }
> >>
> >> + dev->lsc_interrupt_mode = dev->requested_lsc_interrupt_mode;
> >
> > I think this would be removed from here and only set once rte_eth_dev_configure succeeds in dpdk_eth_dev_port_config as
> mentioned earlier?
> >
> >> +
> >> netdev->n_txq = dev->requested_n_txq;
> >> netdev->n_rxq = dev->requested_n_rxq;
> >>
> >
> > It could be useful to report the LSC mode configured for the port also as part of the port status, something like
> >
> > @@ -2781,6 +2783,8 @@ netdev_dpdk_get_status(const struct netdev *netdev, struct smap *args)
> > dev_info.max_hash_mac_addrs);
> > smap_add_format(args, "max_vfs", "%u", dev_info.max_vfs);
> > smap_add_format(args, "max_vmdq_pools", "%u", dev_info.max_vmdq_pools);
> > + smap_add_format(args, "lsc_mode", "%s",
> > + dev->lsc_interrupt_mode ? "Interrupt" : "PMD");
> >
> > Thoughts?
>
> We have this in 'netdev_dpdk_get_config()'. Do you think we need this
> in two places? Also, 'netdev_dpdk_get_status()' is more like HW
> specific invariants. (Not sure why we're placing these values in 'status',
> it's a bit strange.)
>
> >
> >> diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml index
> >> 0c6a43d..3c9e637 100644
> >> --- a/vswitchd/vswitch.xml
> >> +++ b/vswitchd/vswitch.xml
> >> @@ -3631,6 +3631,23 @@ ovs-vsctl add-port br0 p0 -- set Interface p0
> >> type=patch options:peer=p1 \
> >> </column>
> >> </group>
> >>
> >> + <group title="Link State Change detection mode">
> >> + <column name="options" key="dpdk-lsc-interrupt"
> >> + type='{"type": "boolean"}'>
> >> + <p>
> >> + Set this value to <code>true</code> to configure interrupt mode
> >> for
> >> + Link State Change (LSC) detection instead of poll mode for the
> >> DPDK
> >> + interface.
> >> + </p>
> >> + <p>
> >> + If this value is not set, poll mode is configured.
> >> + </p>
> >> + <p>
> >> + This parameter has an effect only on netdev dpdk interfaces.
> >> + </p>
> >> + </column>
> >> + </group>
> >> +
> >> <group title="Common Columns">
> >> The overall purpose of these columns is described under
> >> <code>Common
> >> Columns</code> at the beginning of this document.
> >> --
> >> 1.9.1
> >>
> >> _______________________________________________
> >> dev mailing list
> >> dev at openvswitch.org
> >> https://mail.openvswitch.org/mailman/listinfo/ovs-dev
> >
> >
> >
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