[ovs-dev] [PATCH] netdev-linux: Fix ingress policing burst rate configuration via tc
Ben Pfaff
blp at ovn.org
Thu Apr 14 16:28:22 UTC 2016
Thanks, I see the re-sent version.
On Thu, Apr 14, 2016 at 09:55:50AM +0200, Miguel Angel Ajo Pelayo wrote:
> Ouch, I wonder what happened. I will retry, sorry about it.
>
> On Thu, Apr 14, 2016 at 1:08 AM, Ben Pfaff <blp at ovn.org> wrote:
> > Thanks for working on this. The original patch, as opposed to the
> > followup quoted below) doesn't seem to have made it to the mailing list
> > archive or to patchwork. Can you resend it?
> >
> > On Wed, Apr 13, 2016 at 12:49:28PM +0200, Miguel Angel Ajo Pelayo wrote:
> >> I verified the 10% / 80% changes with netperf, it's unable to sustain 10Mbps
> >> without at least a 8Mbit burst. I've seen recommendations from cisco to use
> >> policing bursts of around 150 to 200%, but I guess that depends on the path
> >> latency or even the implementation.
> >>
> >> My netperf tests were in-host.
> >>
> >>
> >>
> >> On Wed, Apr 13, 2016 at 12:44 PM, Miguel Angel Ajo <majopela at redhat.com> wrote:
> >> > The tc_police structure was filled with a value calculated in bits
> >> > instead of bytes while bytes were expected. This led the setting
> >> > of an x8 higher burst value.
> >> >
> >> > Documentation and defaults have been corrected acordingly to minimize
> >> > nuisances on users sticking to the defaults.
> >> >
> >> > The suggested burst value is now 80% of policing rate to make sure
> >> > TCP works correctly.
> >> >
> >> > Signed-off-by: Miguel Angel Ajo <majopela at redhat.com>
> >> > Tested-by: Miguel Angel Ajo <majopela at redhat.com>
> >> > ---
> >> > FAQ.md | 2 +-
> >> > lib/netdev-linux.c | 14 ++++----------
> >> > vswitchd/vswitch.xml | 4 ++--
> >> > 3 files changed, 7 insertions(+), 13 deletions(-)
> >> >
> >> > diff --git a/FAQ.md b/FAQ.md
> >> > index 04ffc84..7dcdb4c 100644
> >> > --- a/FAQ.md
> >> > +++ b/FAQ.md
> >> > @@ -1124,7 +1124,7 @@ A: A policing policy can be configured on an interface to drop packets
> >> > generate to 10Mbps:
> >> >
> >> > ovs-vsctl set interface vif1.0 ingress_policing_rate=10000
> >> > - ovs-vsctl set interface vif1.0 ingress_policing_burst=1000
> >> > + ovs-vsctl set interface vif1.0 ingress_policing_burst=8000
> >> >
> >> > Traffic policing can interact poorly with some network protocols and
> >> > can have surprising results. The "Ingress Policing" section of
> >> > diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
> >> > index a7d7ac7..a2b6b8a 100644
> >> > --- a/lib/netdev-linux.c
> >> > +++ b/lib/netdev-linux.c
> >> > @@ -2045,7 +2045,7 @@ netdev_linux_set_policing(struct netdev *netdev_,
> >> > int error;
> >> >
> >> > kbits_burst = (!kbits_rate ? 0 /* Force to 0 if no rate specified. */
> >> > - : !kbits_burst ? 1000 /* Default to 1000 kbits if 0. */
> >> > + : !kbits_burst ? 8000 /* Default to 8000 kbits if 0. */
> >> > : kbits_burst); /* Stick with user-specified value. */
> >> >
> >> > ovs_mutex_lock(&netdev->mutex);
> >> > @@ -4720,21 +4720,15 @@ tc_add_policer(struct netdev *netdev,
> >> > tc_police.mtu = mtu;
> >> > tc_fill_rate(&tc_police.rate, ((uint64_t) kbits_rate * 1000)/8, mtu);
> >> >
> >> > - /* The following appears wrong in two ways:
> >> > - *
> >> > - * - tc_bytes_to_ticks() should take "bytes" as quantity for both of its
> >> > - * arguments (or at least consistently "bytes" as both or "bits" as
> >> > - * both), but this supplies bytes for the first argument and bits for the
> >> > - * second.
> >> > - *
> >> > - * - In networking a kilobit is usually 1000 bits but this uses 1024 bits.
> >> > + /* The following appears wrong in one way: In networking a kilobit is
> >> > + * usually 1000 bits but this uses 1024 bits.
> >> > *
> >> > * However if you "fix" those problems then "tc filter show ..." shows
> >> > * "125000b", meaning 125,000 bits, when OVS configures it for 1000 kbit ==
> >> > * 1,000,000 bits, whereas this actually ends up doing the right thing from
> >> > * tc's point of view. Whatever. */
> >> > tc_police.burst = tc_bytes_to_ticks(
> >> > - tc_police.rate.rate, MIN(UINT32_MAX / 1024, kbits_burst) * 1024);
> >> > + tc_police.rate.rate, MIN(UINT32_MAX / 1024, kbits_burst) * 1024 / 8);
> >> >
> >> > tcmsg = tc_make_request(netdev, RTM_NEWTFILTER,
> >> > NLM_F_EXCL | NLM_F_CREATE, &request);
> >> > diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
> >> > index 7d6976f..fca238d 100644
> >> > --- a/vswitchd/vswitch.xml
> >> > +++ b/vswitchd/vswitch.xml
> >> > @@ -2434,7 +2434,7 @@
> >> >
> >> > <column name="ingress_policing_burst">
> >> > <p>Maximum burst size for data received on this interface, in kb. The
> >> > - default burst size if set to <code>0</code> is 1000 kb. This value
> >> > + default burst size if set to <code>0</code> is 8000 kbit. This value
> >> > has no effect if <ref column="ingress_policing_rate"/>
> >> > is <code>0</code>.</p>
> >> > <p>
> >> > @@ -2442,7 +2442,7 @@
> >> > which is important for protocols like TCP that react severely to
> >> > dropped packets. The burst size should be at least the size of the
> >> > interface's MTU. Specifying a value that is numerically at least as
> >> > - large as 10% of <ref column="ingress_policing_rate"/> helps TCP come
> >> > + large as 80% of <ref column="ingress_policing_rate"/> helps TCP come
> >> > closer to achieving the full rate.
> >> > </p>
> >> > </column>
> >> > --
> >> > 1.8.3.1
> >> >
> >> > This patch fixes the burst setting of the ingress policing on netdev-linux, and
> >> > corrects the documentation recommendations accordingly.
> >> >
> >> > Before the patch we had:
> >> >
> >> >
> >> > # ovs-vsctl -- --may-exist add-port br-int test-port -- set Interface test-port type=internal
> >> > # ovs-vsctl set interface test-port ingress_policing_rate=10000
> >> > # ovs-vsctl set interface test-port ingress_policing_burst=1000
> >> > # tc filter show dev test-port parent ffff:
> >> > filter protocol all pref 49 basic
> >> > filter protocol all pref 49 basic handle 0x1
> >> > police 0x1 rate 10000Kbit burst 1000Kb mtu 64Kb action drop overhead 0b
> >> > ref 1 bind 1
> >> >
> >> > After the patch we have:
> >> >
> >> > # ovs-vsctl set interface test-port ingress_policing_rate=10000
> >> > # ovs-vsctl set interface test-port ingress_policing_burst=1000
> >> > # tc filter show dev test-port parent ffff:
> >> > filter protocol all pref 49 basic
> >> > filter protocol all pref 49 basic handle 0x1
> >> > police 0x2 rate 10000Kbit burst 125Kb mtu 64Kb action drop overhead 0b
> >> > ref 1 bind 1
> >> >
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