Re: [PATCH mptcp-next 1/3] mptcp: sched: penalise a slow subflow by halving its cwnd

[Matthieu Baerts <matttbe@kernel.org>]

Hi Shardul,

Thank you for your reply!

On 07/08/2026 17:18, Shardul Bankar wrote:
> On Wed, 2026-07-29 at 13:49 +0200, Matthieu Baerts wrote:
>> On 26/07/2026 07:55, Shardul Bankar wrote:

(...)

>>> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
>>> index da40c6f3705f..2bf801292563 100644
>>> --- a/net/mptcp/protocol.h
>>> +++ b/net/mptcp/protocol.h
>>> @@ -587,6 +587,7 @@ struct mptcp_subflow_context {
>>>                 __unused : 8;
>>>         bool    data_avail;
>>>         bool    scheduled;
>>> +       bool    penalise;           /* scheduler flagged this
>>> subflow for cwnd halving */
>>
>> (If you don't need to read this locklessly, then you can probably use
>> one unused bit.)
>>
> 
> It is written under two locks (set in the scheduler under the msk lock,
> cleared in the push path under the subflow lock), so a shared bitfield
> word would race on the read-modify-write, and I kept it a bool for that
> reason. If you see a single-lock way to do it, I am glad to move it to
> a bit.

I didn't check all entries from the bitfield a few lines above, but are
they not also written under the subflow lock? (but maybe not under the
msk lock)

But if you saw a risk, fine to keep it like that.

Cheers,
Matt
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