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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Yibo Zhao <yiboz@codeaurora.org>, ath10k@lists.infradead.org
Cc:     linux-wireless@vger.kernel.org, Yibo Zhao <yiboz@codeaurora.org>
Subject: Re: [PATCH 4/4] mac80211: Sync airtime weight sum with per AC synced sta airtime weight together
In-Reply-To: <1568639388-27291-4-git-send-email-yiboz@codeaurora.org>
References: <1568639388-27291-1-git-send-email-yiboz@codeaurora.org> <1568639388-27291-4-git-send-email-yiboz@codeaurora.org>
Date:   Tue, 17 Sep 2019 23:24:04 +0200
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Yibo Zhao <yiboz@codeaurora.org> writes:

> Global airtime weight sum is updated only when txq is added/removed
> from rbtree. If upper layer configures sta weight during high load,
> airtime weight sum will not be updated since txq is most likely on the
> tree. It could a little late for upper layer to reconfigure sta weight
> when txq is already in the rbtree. And thus, incorrect airtime weight sum
> will lead to incorrect global virtual time calculation as well as global
> airtime weight sum overflow of airtime weight sum during txq removed.
>
> Hence, need to update airtime weight sum upon receiving event for
> configuring sta weight once sta's txq is on the rbtree.
>
> Besides, if airtime weight sum of ACs and sta weight is synced under the
> same per AC lock protection, there can be a very short window causing
> incorrct airtime weight sum calculation as below:
>
>     active_txq_lock_VO                          .
>     VO weight sum is syncd=09=09=09.
>     sta airtime weight sum is synced=09=09.
>     active_txq_unlock_VO=09=09=09.
>     .=09=09=09=09=09=09.
>     active_txq_lock_VI    =09=09=09.
>     VI weight sum is syncd=09=09=09.
>     sta airtime weight sum=09=09active_txq_lock_BE
>     active_txq_unlock_VI=09      Remove txq and thus sum
>     .=09=09=09=09      is calculated with synced
>     .=09=09=09=09      sta airtime weight
>     .=09=09=09=09=09active_txq_unlock_BE
>
> So introduce a per ac synced station airtime weight synced with per
> AC synced weight sum together. And the per-AC station airtime weight
> is used to calculate weight sum.
>
> Signed-off-by: Yibo Zhao <yiboz@codeaurora.org>
> ---
>  net/mac80211/cfg.c      | 27 +++++++++++++++++++++++++--
>  net/mac80211/sta_info.c |  6 ++++--
>  net/mac80211/sta_info.h |  3 +++
>  net/mac80211/tx.c       |  4 ++--
>  4 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
> index d65aa01..4b420bb 100644
> --- a/net/mac80211/cfg.c
> +++ b/net/mac80211/cfg.c
> @@ -1284,7 +1284,8 @@ static int sta_apply_parameters(struct ieee80211_lo=
cal *local,
>  =09int ret =3D 0;
>  =09struct ieee80211_supported_band *sband;
>  =09struct ieee80211_sub_if_data *sdata =3D sta->sdata;
> -=09u32 mask, set;
> +=09u32 mask, set, tid, ac;
> +=09struct txq_info *txqi;
> =20
>  =09sband =3D ieee80211_get_sband(sdata);
>  =09if (!sband)
> @@ -1452,8 +1453,30 @@ static int sta_apply_parameters(struct ieee80211_l=
ocal *local,
>  =09if (ieee80211_vif_is_mesh(&sdata->vif))
>  =09=09sta_apply_mesh_params(local, sta, params);
> =20
> -=09if (params->airtime_weight)
> +=09if (params->airtime_weight &&
> +=09    params->airtime_weight !=3D sta->airtime_weight) {
> +=09=09for (ac =3D 0; ac < IEEE80211_NUM_ACS; ac++) {
> +=09=09=09spin_lock_bh(&local->active_txq_lock[ac]);
> +=09=09=09for (tid =3D 0; tid < IEEE80211_NUM_TIDS + 1; tid++) {
> +=09=09=09=09if (!sta->sta.txq[tid] ||
> +=09=09=09=09    ac !=3D ieee80211_ac_from_tid(tid))
> +=09=09=09=09=09continue;
> +
> +=09=09=09=09sta->airtime_weight_synced[ac] =3D
> +=09=09=09=09=09=09=09params->airtime_weight;
> +
> +=09=09=09=09txqi =3D to_txq_info(sta->sta.txq[tid]);
> +=09=09=09=09if (RB_EMPTY_NODE(&txqi->schedule_order))
> +=09=09=09=09=09continue;
> +
> +=09=09=09=09local->airtime_weight_sum[ac] =3D local->airtime_weight_sum[=
ac] +
> +=09=09=09=09=09=09=09=09params->airtime_weight -
> +=09=09=09=09=09=09=09=09sta->airtime_weight;
> +=09=09=09}
> +=09=09=09spin_unlock_bh(&local->active_txq_lock[ac]);
> +=09=09}
>  =09=09sta->airtime_weight =3D params->airtime_weight;

With this, airtime_weight is basically only used to return to and from
userspace, right? I.e., after the above loop has run, it will match the
contents of airtime_weight_synced; so why not just turn airtime_weight
into  a per-ac array? You could just use airtime_weight[0] as the value
to return to userspace...

-Toke