On 2018年09月13日 03:11, Willem de Bruijn wrote:
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.
Consider we may have interrupt moderation in the future, I tend to use
set_coalesce. Otherwise we may need two steps to enable moderation:
- tx-napi on
- set_coalesce
Thanks
