Message-ID: <a5151441bdfe02cb11043aa0786185b8ee3c3ee9.camel@sipsolutions.net>
Subject: Re: [PATCH] mac80211: Change default tx_sk_pacing_shift to 7
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@toke.dk>
Cc:     linux-wireless@vger.kernel.org,
        Ben Greear <greearb@candelatech.com>,
        Grant Grundler <grundler@google.com>,
        Kalle Valo <kvalo@codeaurora.org>, wgong@qti.qualcomm.com,
        ath10k@lists.infradead.org, wgong@codeaurora.org,
        Kan Yan <kyan@google.com>
Date:   Fri, 22 Feb 2019 14:07:36 +0100
In-Reply-To: <87lg28vup0.fsf@toke.dk>
References: <20190221172936.21816-1-toke@redhat.com>
         <E1gx9x3-0002j0-1J@sipsolutions.net> <87lg28vup0.fsf@toke.dk>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On Fri, 2019-02-22 at 14:06 +0100, Toke Høiland-Jørgensen wrote:
> Johannes Berg <johannes@sipsolutions.net> writes:
> 
> > Toke Høiland-Jørgensen wrote:
> > 
> > > When we did the original tests for the optimal value of sk_pacing_shift, we
> > > came up with 6 ms of buffering as the default. Sadly, 6 is not a power of
> > > two, so when picking the shift value I erred on the size of less buffering
> > > and picked 4 ms instead of 8. This was probably wrong; those 2 ms of extra
> > > buffering makes a larger difference than I thought.
> > > 
> > > So, change the default pacing shift to 7, which corresponds to 8 ms of
> > > buffering. The point of diminishing returns really kicks in after 8 ms, and
> > > so having this as a default should cut down on the need for extensive
> > > per-device testing and overrides needed in the drivers.
> > > 
> > > Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> > 
> > Patch applied to wireless.git, thanks.
> > 
> > a41f56b9a17a (HEAD -> mac80211) mac80211: Change default
> > tx_sk_pacing_shift to 7

This mess came from Kalle's tool btw, so I can't really use it yet :-)

> Cool, thanks! What's the easiest way to backport this? I figure it's
> easier to just update sk_pacing_shift_update() in tx.c for 4.19 (which
> predates the addition of the driver override hook); shall I just send a
> separate patch to stable for that? Or do we need to backport the driver
> override hook as well?

Just update the value, no need to backport the hook.

johannes