From: Jakub Kicinski <jakub.kicinski@netronome.com>
To: Robert Beckett <bob.beckett@collabora.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
davem@davemloft.net, netdev@vger.kernel.org, nhorman@redhat.com,
sassmann@redhat.com, Aaron Brown <aaron.f.brown@intel.com>
Subject: Re: [net-next 2/7] igb: add rx drop enable attribute
Date: Thu, 17 Oct 2019 10:40:25 -0700 [thread overview]
Message-ID: <20191017104025.31f00c97@cakuba.netronome.com> (raw)
In-Reply-To: <c04a2fbd630e91435eab985abfaf3bcb6a8d60d5.camel@collabora.com>
On Thu, 17 Oct 2019 18:04:22 +0100, Robert Beckett wrote:
> On Thu, 2019-10-17 at 08:44 -0700, Jakub Kicinski wrote:
> > 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.beckett@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.beckett@collabora.com>
> > > > > Tested-by: Aaron Brown <aaron.f.brown@intel.com>
> > > > > Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@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?
>
> Correct.
> Honestly I personally considered it a bug when I first saw it.
>
> see e6bdb6fefc590
>
> Specifically it enables dropping of frames if multiple queues are in
> use, ostensibly to prevent head of line blocking between the different
> rx queues.
>
> This patch says that that should be a user choice, defaulting to the
> old behaviour.
I'd say just always enable it then. Honestly if it's statically enabled
with multi queue (which I presume is the default?) then there's no need
for us to ponder the uAPI questions. I can't think of anyone flipping
that flag to disabled...
Flow control is supposed to prevent _all_ drops it can, AFAIU.
If we get an actual user request to change it we can revisit.
next prev parent reply other threads:[~2019-10-17 17:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 23:47 [net-next 0/7][pull request] 1GbE Intel Wired LAN Driver Updates 2019-10-16 Jeff Kirsher
2019-10-16 23:47 ` [net-next 1/7] igb/igc: Don't warn on fatal read failures when the device is removed Jeff Kirsher
2019-10-16 23:58 ` Jakub Kicinski
2019-10-16 23:47 ` [net-next 2/7] igb: add rx drop enable attribute Jeff Kirsher
2019-10-16 23:55 ` Jakub Kicinski
2019-10-17 11:24 ` Robert Beckett
2019-10-17 15:44 ` Jakub Kicinski
2019-10-17 17:04 ` Robert Beckett
2019-10-17 17:40 ` Jakub Kicinski [this message]
2019-10-16 23:47 ` [net-next 3/7] igc: Add SCTP CRC checksumming functionality Jeff Kirsher
2019-10-16 23:47 ` [net-next 4/7] e1000e: Add support for S0ix Jeff Kirsher
2019-10-17 0:02 ` Jakub Kicinski
2019-10-17 5:09 ` Neftin, Sasha
2019-10-16 23:47 ` [net-next 5/7] igc: Add set_rx_mode support Jeff Kirsher
2019-10-16 23:47 ` [net-next 6/7] igc: Add Rx checksum support Jeff Kirsher
2019-10-16 23:47 ` [net-next 7/7] igc: Clean up unused shadow_vfta pointer Jeff Kirsher
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