Re: [PATCH] tcp: Implement a two-level initial RTO as per draft RFC 2988bis-02.

Am 19.05.2011 um 08:42 schrieb tsuna:

On Wed, May 18, 2011 at 11:36 PM, Alexander Zimmermann
[off-list ref] wrote:

quoted

If you set the initRTO=0.1s, it's good for me but bad for the rest of the
world. That's the difference.

Or do you want to implement a lower barrier of 1sec so that you can ensure
that nobody set the initRTO lower than 1s?

Oh, I see.  Yes, there is a lower bound (and an upper bound) on what
values the kernel will accept as initRTO.  In the patch "Implement a
two-level initial RTO as per draft RFC 2988bis-02" above, I re-used
TCP_RTO_MIN and TCP_RTO_MAX in net/ipv4/sysctl_net_ipv4.c in order to
prevent users from setting a minRTO that's outside this range.  They
are defined as follows in tcp.h:

#define TCP_RTO_MAX     ((unsigned)(120*HZ))
#define TCP_RTO_MIN     ((unsigned)(HZ/5))

So we're talking about a [200ms ; 120s] range no matter what.

Why is 200ms a valid lower bound for initRTO? I'm aware of
measurements that 1s is save for Internet, but I don't know of any
studies that 200ms is save... 

-- 
Benoit "tsuna" Sigoure
Software Engineer @ www.StumbleUpon.com

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