netdev - Re: [PATCH] make _minimum_ TCP retransmission timeout configurable

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Message-ID: <OFD89921DD.675E7B9A-ON65257347.001C5D22-65257347.001D84A0@in.ibm.com>
Date:	Thu, 30 Aug 2007 10:52:24 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>, ian.mcdonald@...di.co.nz,
	ilpo.jarvinen@...sinki.fi, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org
Subject: Re: [PATCH] make _minimum_ TCP retransmission timeout configurable

Hi Rick,

> > From: Rick Jones <rick.jones2@...com>
> >>The trace I've been sent shows clean RTTs ranging from ~200
milliseconds
> >>to ~7000 milliseconds.
> >
> >
> > Thanks for the info.
> >
> > It's pretty easy to generate examples where we might have some sockets
> > talking over interfaces on such a network and others which are not.
> > Therefore, if we do this, a per-route metric is probably the best bet.
>
> FWIW, the places where I've seen this come-up thusfar are where we have
> a sort of "gateway" or front-end system which is connected on one side
> to the cellphone network with the bad delays, and on the other side is
> connected to an internal network where actual losses leading to RTO's
> are epsilon.  Certainly something which could make a per-route decision
> would work there and probably quite well, though a simple sysctl does
> seem to be sufficient and would touch fewer places.
>
> Do you think it is still worthwhile for me to rework the initial patch
> to use CTL_UNNUMBERED?

You could add following cleanup:

static int proc_tcp_rto_min(ctl_table *ctl, int write, struct file *filp,
                                        void __user *buffer, size_t *lenp,
loff_t *ppos)
{
      int *valp = ctl->data;
      int oldval = *valp;
      int ret;

      ret = proc_dointvec_ms_jiffies(ctl, write, filp, buffer, lenp, ppos);
      if (ret)
            return ret;

      /* some bounds checking would be in order */
      if (write && *valp != oldval) {
            if (*valp < (int)TCP_RTO_MIN || *valp > (int)TCP_RTO_MAX) {
                  *valp = oldval;
                  ret = -EINVAL;
             }
      }
      return ret;
}

Also, isn't it enough to use u32 for valp/oldval and remove the "(int)"
typecasts?

Thanks,

- KK

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