On Thu, 17 Oct 2019 12:24:03 +0100, Robert Beckett wrote: > On Wed, 2019-10-16 at 16:55 -0700, Jakub Kicinski wrote: > > On Wed, 16 Oct 2019 16:47:06 -0700, Jeff Kirsher wrote: > > > From: Robert Beckett <bob.beck...@collabora.com> > > > > > > To allow userland to enable or disable dropping packets when > > > descriptor > > > ring is exhausted, add RX_DROP_EN private flag. > > > > > > This can be used in conjunction with flow control to mitigate > > > packet storms > > > (e.g. due to network loop or DoS) by forcing the network adapter to > > > send > > > pause frames whenever the ring is close to exhaustion. > > > > > > By default this will maintain previous behaviour of enabling > > > dropping of > > > packets during ring buffer exhaustion. > > > Some use cases prefer to not drop packets upon exhaustion, but > > > instead > > > use flow control to limit ingress rates and ensure no dropped > > > packets. > > > This is useful when the host CPU cannot keep up with packet > > > delivery, > > > but data delivery is more important than throughput via multiple > > > queues. > > > > > > Userland can set this flag to 0 via ethtool to disable packet > > > dropping. > > > > > > Signed-off-by: Robert Beckett <bob.beck...@collabora.com> > > > Tested-by: Aaron Brown <aaron.f.br...@intel.com> > > > Signed-off-by: Jeff Kirsher <jeffrey.t.kirs...@intel.com> > > > > How is this different than enabling/disabling flow control.. > > > > ethtool -a/-A > > Enabling flow control enables the advertisement of flow control > capabilites and allows negotiation with link partner.
More or less. If autoneg is on it controls advertised bits, if autoneg is off it controls the enabled/disable directly. > It does not dictate under which circumstances those pause frames will > be emitted. So you're saying even with pause frames on igb by default will not backpressure all the way to the wire if host RX ring is full/fill ring is empty? > This patch enables an igb specific feature that can cause flow control > to be used. The default behaviour is to drop packets if the rx ring > buffer fills. This flag tells the driver instead to emit pause frames > and not drop packets, which is useful when reliable data delivery is > more important than throughput. The feature looks like something easily understood with a standard NIC model in mind. Therefore it should have a generic config knob not a private flag.
