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Message-ID: <CAK6E8=dhkD89=buv15VwaYewgh2FHByHAGBAVK-5t2ikjs_nKA@mail.gmail.com>
Date: Thu, 8 Sep 2016 08:31:46 -0700
From: Yuchung Cheng <ycheng@...gle.com>
To: David Miller <davem@...emloft.net>
Cc: francisyyan@...il.com, netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next 1/2] tcp: measure rwnd-limited time
On Wed, Sep 7, 2016 at 5:27 PM, David Miller <davem@...emloft.net> wrote:
>
> From: "Francis Y. Yan" <francisyyan@...il.com>
> Date: Tue, 6 Sep 2016 18:32:40 -0700
>
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index 7be9b12..f5b588e 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -176,6 +176,7 @@ struct tcp_sock {
> > * were acked.
> > */
> > struct u64_stats_sync syncp; /* protects 64bit vars (cf tcp_get_info()) */
> > + seqcount_t seqcnt; /* proctects rwnd-limited-related vars, etc. */
> >
> > u32 snd_una; /* First byte we want an ack for */
> > u32 snd_sml; /* Last byte of the most recently transmitted small packet */
> > @@ -204,6 +205,8 @@ struct tcp_sock {
> >
> > u32 window_clamp; /* Maximal window to advertise */
> > u32 rcv_ssthresh; /* Current window clamp */
> > + struct skb_mstamp rwnd_limited_ts; /* Last timestamp limited by rwnd */
> > + u64 rwnd_limited; /* Total time (us) limited by rwnd */
> >
> > /* Information of the most recently (s)acked skb */
> > struct tcp_rack {
>
> I understand completely the usefulness of this change, but wow that is a lot of
> new TCP socket space taken up just to export some time values in tcp_info for
> debugging and statistics.
Thanks for raising the concern. The space requirement and timing
resolution should indeed be justified better on the motivation and the
dev plan. We would resubmit a v2 with a cover letter detailing those.
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