From: Eric Dumazet <eric.dumazet@gmail.com>
To: Chris Friesen <cfriesen@nortel.com>
Cc: netdev@vger.kernel.org, Linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: seeing strange values for tcp sk_rmem_alloc
Date: Thu, 03 Dec 2009 18:04:14 +0100 [thread overview]
Message-ID: <4B17EF8E.60704@gmail.com> (raw)
In-Reply-To: <4B17ED8D.7050409@nortel.com>
Chris Friesen a écrit :
> 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
Might be because you use loopback device ? ;)
ifconfig lo | grep MTU
UP LOOPBACK RUNNING MTU:16436 Metric:1
After a while (when hitting rcvbuf limit), tcp stack performs skb collapses, to reduce ram usage.
next prev parent reply other threads:[~2009-12-03 17:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-12-01 16:16 seeing strange values for tcp sk_rmem_alloc Chris Friesen
2009-12-01 16:18 ` Chris Friesen
2009-12-01 16:58 ` Eric Dumazet
2009-12-01 17:28 ` Chris Friesen
2009-12-01 17:52 ` Eric Dumazet
2009-12-03 16:55 ` Chris Friesen
2009-12-03 17:04 ` Eric Dumazet [this message]
2009-12-03 21:40 ` Chris Friesen
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