From: Bill Fink <billfink@mindspring•com>
To: " Ilpo Järvinen " <ilpo.jarvinen@helsinki•fi>
Cc: Evgeniy Polyakov <zbr@ioremap•net>,
bert hubert <bert.hubert@netherlabs•nl>,
"H. Willstrand" <h.willstrand@gmail•com>,
Netdev <netdev@vger•kernel.org>
Subject: Re: sendfile()? Re: SO_LINGER dead: I get an immediate RST on 2.6.24?
Date: Tue, 13 Jan 2009 00:31:08 -0500 [thread overview]
Message-ID: <20090113003108.72860b5c.billfink@mindspring.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0901121111420.24748@wrl-59.cs.helsinki.fi>
On Mon, 12 Jan 2009, Ilpo Järvinen wrote:
> On Sun, 11 Jan 2009, Bill Fink wrote:
>
> > On Mon, 12 Jan 2009, Evgeniy Polyakov wrote:
> >
> > > On Mon, Jan 12, 2009 at 12:08:24AM +0100, bert hubert (bert.hubert@netherlabs•nl) wrote:
> > > > I fully understand. Sometimes I have to talk to stupid devices though. What
> > > > I do find is the TCP_INFO ioctl, which offers this field in struct tcp_info:
> > > >
> > > > __u32 tcpi_unacked;
> > > >
> > > > Which comes from:
> > > >
> > > > struct tcp_sock {
> > > > ...
> > > > u32 packets_out; /* Packets which are "in flight" */
> > > > ...
> > > > }
> > > >
> > > > If this becomes 0, perhaps this might tell me everything I sent was acked?
> > >
> > > 0 means that there are noin-flight packets, which is effectively number
> > > of unacked packets. So if your application waits for this field to
> > > become zero, it will wait for all sent packets to be acked.
> >
> > I use this type of strategy in nuttcp, and it seems to work fine.
> > I have a loop with a small delay and a check of tcpi_unacked, and
> > break out of the loop if tcpi_unacked becomes 0 or a defined timeout
> > period has passed.
>
> Checking tcpi_unacked alone won't be reliable. The peer might be slow
> enough to advertize zero window for a short period of time and during
> that period you would have packets_out zero...
I'll keep this in mind for the future, although it doesn't seem to
be a significant issue in practice. I use this scheme to try and
account for the tcpi_total_retrans for the data stream, so if this
corner case was hit, it would mean an under reporting of the total
TCP retransmissions for the nuttcp test.
If I understand you correctly, to hit this corner case, just after
the final TCP write, there would have to be no packets in flight
together with a zero TCP window. To make it more bullet-proof, I
guess after seeing a zero tcpi_unacked, an additional small delay
should be performed, and then rechecking for a zero tcpi_unacked.
I don't see anything else obvious (to me anyway) in the tcp_info
that would be particularly helpful in handling this.
-Thanks
-Bill
next prev parent reply other threads:[~2009-01-13 5:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-11 21:23 SO_LINGER dead: I get an immediate RST on 2.6.24? bert hubert
2009-01-11 22:08 ` H. Willstrand
2009-01-11 22:45 ` sendfile()? " bert hubert
2009-01-11 22:54 ` Evgeniy Polyakov
2009-01-11 23:08 ` bert hubert
2009-01-11 23:18 ` Evgeniy Polyakov
2009-01-12 4:50 ` Bill Fink
2009-01-12 9:18 ` Ilpo Järvinen
2009-01-13 5:31 ` Bill Fink [this message]
2009-02-13 17:02 ` Jeremy Jackson
2009-02-20 18:10 ` Bill Fink
-- strict thread matches above, loose matches on Subject: below --
2009-01-13 6:32 Herbert Xu
2009-01-13 6:56 ` Bill Fink
2009-01-13 7:01 ` Herbert Xu
2009-01-14 7:43 ` Bill Fink
2009-01-14 8:29 ` Herbert Xu
2009-01-14 9:05 ` Bill Fink
2009-01-14 11:30 ` Herbert Xu
2009-01-15 6:33 ` Bill Fink
2009-01-13 7:06 ` Rick Jones
2009-01-14 8:05 ` Bill Fink
2009-01-14 8:08 ` Rick Jones
2009-01-14 8:32 ` Bill Fink
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