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From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Subject: Re: [PATCH v9 4/4] mac80211: Use Airtime-based Queue Limits (AQL) on
 packet dequeue
In-Reply-To: <CA+iem5tF+TN-osfGxu=EU5Xt1Uq+PcKgBVaoAmZY3a3JzS5JzQ@mail.gmail.com>
References: <157382403672.580235.12525941420808058808.stgit@toke.dk>
 <157382404118.580235.14216392299709793599.stgit@toke.dk>
 <CA+iem5tF+TN-osfGxu=EU5Xt1Uq+PcKgBVaoAmZY3a3JzS5JzQ@mail.gmail.com>
Date: Sat, 16 Nov 2019 12:55:23 +0100
Message-ID: <87y2wgjas4.fsf@toke.dk>
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To: Kan Yan <kyan@google.com>
Cc: Rajkumar Manoharan <rmanohar@codeaurora.org>, Kevin Hayes <kevinhayes@google.com>, Make-Wifi-fast <make-wifi-fast@lists.bufferbloat.net>, linux-wireless <linux-wireless@vger.kernel.org>, ath10k@lists.infradead.org, John Crispin <john@phrozen.org>, Johannes Berg <johannes@sipsolutions.net>, Lorenzo Bianconi <lorenzo@kernel.org>, Felix Fietkau <nbd@nbd.name>

Kan Yan <kyan@google.com> writes:

>> +static inline u16
>> +ieee80211_info_set_tx_time_est(struct ieee80211_tx_info *info, u16 tx_time_est)
>> +{
>> +       /* We only have 10 bits in tx_time_est, so store airtime
>> +        * in increments of 4us and clamp the maximum to 2**12-1
>> +        */
>> +       info->tx_time_est = min_t(u16, tx_time_est, 4095) >> 2;
>> +       return info->tx_time_est;
>> +}
>> +
>> +static inline u16
>> +ieee80211_info_get_tx_time_est(struct ieee80211_tx_info *info)
>> +{
>> +       return info->tx_time_est << 2;
>> +}
>> +
>
> set_tx_time_est() returns airtime in different units (4us) than
> get_tx_time_est(), this will cause the pending_airtime out of whack.

Huh, you're quite right; oops! I meant to shift that back before
returning. Will fix.

> Given the fact that AQL is only tested in very limited platforms,
> should we set the default to disabled by removing this change in the
> next update?
>
> -       local->airtime_flags = AIRTIME_USE_TX | AIRTIME_USE_RX;
> +
> +       local->airtime_flags = AIRTIME_USE_TX |
> +                              AIRTIME_USE_RX |
> +                              AIRTIME_USE_AQL;
> +       local->aql_threshold = IEEE80211_AQL_THRESHOLD;
> +       atomic_set(&local->aql_total_pending_airtime, 0);

Well, we have the whole -rc series to get more testing in if we merge it
as-is. It's up to the maintainers, of course, but I would be in favour
of merging as-is, then optionally backing out the default before the
final release if problems do turn up. But I would hope that the limits
are sufficiently conservative that it would not result in any problems :)

-Toke


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