On Wed, Sep 12, 2018 at 2:16 PM Florian Fainelli <f.faine...@gmail.com> wrote: > > > > On 9/12/2018 11:07 AM, Willem de Bruijn wrote: > > On Wed, Sep 12, 2018 at 1:42 PM Florian Fainelli <f.faine...@gmail.com> > > wrote: > >> > >> > >> > >> On 9/9/2018 3:44 PM, Willem de Bruijn wrote: > >>> From: Willem de Bruijn <will...@google.com> > >>> > >>> Implement ethtool .set_coalesce (-C) and .get_coalesce (-c) handlers. > >>> Interrupt moderation is currently not supported, so these accept and > >>> display the default settings of 0 usec and 1 frame. > >>> > >>> Toggle tx napi through a bit in tx-frames. So as to not interfere > >>> with possible future interrupt moderation, use bit 10, well outside > >>> the reasonable range of real interrupt moderation values. > >>> > >>> Changes are not atomic. The tx IRQ, napi BH and transmit path must > >>> be quiesced when switching modes. Only allow changing this setting > >>> when the device is down. > >> > >> Humm, would not a private ethtool flag to switch TX NAPI on/off be more > >> appropriate rather than use the coalescing configuration API here? > > > > What do you mean by private ethtool flag? A new field in ethtool > > --features (-k)? > > I meant using ethtool_drvinfo::n_priv_flags, ETH_SS_PRIV_FLAGS and then > ETHTOOL_GFPFLAGS and ETHTOOL_SPFLAGS to control the toggling of that > private flag. mlx5 has a number of privates flags for instance.
Interesting, thanks! I was not at all aware of those ethtool flags. Am having a look. It definitely looks promising. > > Configurable napi-tx is not a common feature across devices. We really > > want virtio-net to also just convert to napi-tx as default, but need a > > way to gradually convert with application opt-out if some workloads > > see regressions. > > The rationale makes sense, no questions about it. > > > There is prior art in interpreting coalesce values as > > more than a direct mapping to usec. The e1000 is one example. > > > > Looked at both e1000 and e1000e and they both have a similar programming > of the HW's interrupt target rate register, which is relevant to > interrupt coalescing, what part of these drivers do you see as doing > something not quite coalescing related? It's all coalescing related, for sure. e1000_set_coalesce just does not translate the tx-usecs values into microsecond latency directly. It modifies both the interrupt throttle rate adapter->itr and interrupt mode adapter->itr_setting, which are initially set in e1000_check_options from module param InterruptThrottleRate. Value 0 disables interrupt moderation. 1 and 3 program a dynamic mode. 2 is an illegal value as is 5..9. 10..10000 converts from usec to interrupt rate/sec. I took tx-napi to be a similar interrupt related option as, say, dynamic conservative mode interrupt moderation.
