netdev - Re: seeing strange values for tcp sk_rmem

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Message-ID: <4B17ED8D.7050409@nortel.com>
Date:	Thu, 03 Dec 2009 10:55:41 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org, Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: seeing strange values for tcp sk_rmem_alloc

On 12/01/2009 11:52 AM, Eric Dumazet wrote:

> But be careful of sender tcp stack : It might be delayed a bit,
> because it waits for receiver to open its window (slow start)
> 
> You probably need something like
> 
> while (1) {
> 	send(fd1, buffer, 2Kbytes);
> 	sleep(2); // let tcp stack flush its write buffers
> 	display_sk_rmem_alloc(fd2);
> }

Ah, that makes a difference.  But the results (see below) still look
odd.  For this test, /proc/sys/net/core/rmem_default is 118784.  For
some reason sk_rmem_alloc gets bumped by 16KB when I only send 2KB of
data, and it drops back down again every 6 packets.

Chris



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