netdev - Re: iproute uses too small of a receive buffer

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Message-ID: <4AE7F4B0.4010007@gmail.com>
Date:	Wed, 28 Oct 2009 08:37:20 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>,
	Stephen Hemminger <shemminger@...tta.com>
CC:	NetDev <netdev@...r.kernel.org>
Subject: Re: iproute uses too small of a receive buffer

Eric Dumazet a écrit :
> Ben Greear a écrit :
>> Probably the right way is to give a cmd-line arg to set the buffer size
>> and also continue if the error is ENOBUFs (but print some error out
>> so users know they have issues).  I can make the attempt if that
>> sounds good to you.
> 
> Real fix is to realloc buffer at receive time, no need for user setting.
> 
> In my testings I saw it reaching 1 Mbyte
> write(2, "REALLOC buflen 8192\n"..., 20) = 20
> write(2, "REALLOC buflen 16384\n"..., 21) = 21
> write(2, "REALLOC buflen 32768\n"..., 21) = 21
> write(2, "REALLOC buflen 65536\n"..., 21) = 21
> write(2, "REALLOC buflen 131072\n"..., 22) = 22
> write(2, "REALLOC buflen 262144\n"..., 22) = 22
> write(2, "REALLOC buflen 524288\n"..., 22) = 22
> 
> 
> [iproute2] realloc buffer in rtnl_listen
> 
> # ip monitor route
> netlink receive error No buffer space available (105)
> Dump terminated 
> 
> Reported-by: Ben Greear<greearb@...delatech.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Oops, this was wrong, Ben was right, sorry...

ENOBUFS errors is a flag to actually report to user that some information was dropped,
not that user supplied buffer at recv() time is not big enough.

I was surprised that buffer could reach 1Mbytes, while RCVBUF was 32768 or so.


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