netdev - Re: [PATCH net v2] tcp: fix mishandling when the sack compression is deferred

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Date: Tue, 30 May 2023 22:31:38 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: fuyuanli <fuyuanli@...iglobal.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Neal Cardwell <ncardwell@...gle.com>, ycheng <ycheng@...gle.com>, toke <toke@...e.dk>, 
	netdev@...r.kernel.org, Weiping Zhang <zhangweiping@...iglobal.com>, 
	Tio Zhang <tiozhang@...iglobal.com>
Subject: Re: [PATCH net v2] tcp: fix mishandling when the sack compression is deferred

On Tue, May 30, 2023 at 10:23 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, May 30, 2023 at 4:19 PM fuyuanli <fuyuanli@...iglobal.com> wrote:
> >
> > In this patch, we mainly do two things which could be separately
> > found as the following links:
> > 1) fix not sending a compressed ack if it's deferred.
> > 2) use the ICSK_ACK_TIMER flag in tcp_sack_compress_send_ack() and
> > tcp_event_ack_sent() in order we can cancel it if it's deferred.
> >
> > Here are more details in the old logic:
> > When sack compression is triggered in the tcp_compressed_ack_kick(),
> > if the sock is owned by user, it will set TCP_DELACK_TIMER_DEFERRED
> > and then defer to the release cb phrase. Later once user releases
> > the sock, tcp_delack_timer_handler() should send a ack as expected,
> > which, however, cannot happen due to lack of ICSK_ACK_TIMER flag.
> > Therefore, the receiver would not sent an ack until the sender's
> > retransmission timeout. It definitely increases unnecessary latency.
> >
> > Fixes: 5d9f4262b7ea ("tcp: add SACK compression")
> > Suggested-by: Eric Dumazet <edumazet@...gle.com>
> > Signed-off-by: fuyuanli <fuyuanli@...iglobal.com>
> > Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> > Link: https://lore.kernel.org/netdev/20230529113804.GA20300@didi-ThinkCentre-M920t-N000/
> > Link: https://lore.kernel.org/netdev/20230530023737.584-1-kerneljasonxing@gmail.com/
> > ---
> > v2:
> > 1) change the commit title and message
> > 2) reuse the delayed ack logic when handling the sack compression
> > as suggested by Eric.
> > 3) "merge" another related patch into this one. See the second link.
>
> No.
>
> This is not the patch I suggested.

I'm confused. You said in the previous email:
"As a bonus, no need to send one patch for net, and another in net-next,
trying to 'fix' issues that should have been fixed cleanly in a single patch."

So we added "introducing ICSK_ACK_TIMER flag for sack compression" to
fix them on top of the patch you suggested.

I can remove the Suggested-by label. For now, I do care about your
opinion on the current patch.

Well...should I give up introducing that flag and then leave that
'issue' behind? :S

Thanks,
Jason