netdev - Re: [PATCH] tcp: reduce the bloat caused by tcp_is_cwnd

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Message-ID: <1393136390.2316.37.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sat, 22 Feb 2014 22:19:50 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Van Jacobson <vanj@...gle.com>
Subject: Re: [PATCH] tcp: reduce the bloat caused by tcp_is_cwnd_limited()

On Sat, 2014-02-22 at 22:40 -0500, Neal Cardwell wrote:

> 
> AFAICT we should keep the expression in there pertaining to
> sysctl_tcp_tso_win_divisor. AFAICT tcp_is_cwnd_limited() is supposed
> to be saying, "are we cwnd limited? that is, is the available cwnd we
> have left at zero, or so small that it is probably only non-zero
> because tcp_tso_should_defer() is trying to accumulate permission to
> send a bigger TSO skb?"
> 
> To implement this, it seems we need to keep the code that checks for
> possible deferral from both the sysctl_tcp_tso_win_divisor code path
> and the tcp_max_tso_deferred_mss() code paths.
> 
> So, to me, the comment "This is the inverse of cwnd check in
> tcp_tso_should_defer" is still relevant (though not very clear).
> 
> So AFAICT we want the patch to be something like:
> 
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -290,8 +290,7 @@ bool tcp_is_cwnd_limited(const struct sock *sk,
> u32 in_flight)
>         left = tp->snd_cwnd - in_flight;
>         if (sk_can_gso(sk) &&
>             left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
> -           left * tp->mss_cache < sk->sk_gso_max_size &&
> -           left < sk->sk_gso_max_segs)
> +           left < sk->xmit_size_goal_segs)
>                 return true;
>         return left <= tcp_max_tso_deferred_mss(tp);
>  }
> 

Sure, I'll send a v2, thanks !



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