netdev - Re: [PATCH] [RFC] tcp: TSQ - do not always throttle.

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Date:	Tue, 17 Jul 2012 19:38:57 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] [RFC] tcp: TSQ - do not always throttle.

Eric Dumazet <eric.dumazet@...il.com> wrote on 07/17/2012 06:40:54 PM:

> > Do not throttle if sysctl_tcp_limit_output_bytes==0.
> >
> > Maybe it is better to throttle earlier in the loop, after
> > calling tcp_init_tso_segs().
> >
>
> I wonder why, and why you put this question in a changelog instead of
> outside of it...
>
> Idea was to avoid setting TSQ_THROTTLED if we break out the loop.

The reason I mentioned it (in the wrong place) is because
I thought this is a likely case and the checks before that
might all pass only to get throttled. Some of the checks
are quite lengthy.

> About disabling TSQ, my initial intent was to instead use a negative
> sysctl_tcp_limit_output_bytes value.
>
> Thats why I have in tcp_transmit_skb() :
>
> skb->destructor = (sysctl_tcp_limit_output_bytes > 0) ?
>         tcp_wfree : sock_wfree;
>
> So I suggest you change the tcp_write_xmit(() test to a single unsigned
> compare :
>
> if (atomic_read(&sk->sk_wmem_alloc) >=
>     (unsigned) sysctl_tcp_limit_output_bytes) {
>
> Also use :
>
> skb->destructor = (sysctl_tcp_limit_output_bytes >= 0) ?
>   tcp_wfree : sock_wfree;
>
> and document the 'negative value disables TSQ' in
> Documentation/networking/ip-sysctl.txt

Sure, will post with this change.

thanks,
- KK

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