netdev - RE: [PATCH V2 5/7] sctp: use limited socket backlog

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Message-ID: <DA586906BA1FFC4384FCFD6429ECE860A45A6A8E@shzsmsx502.ccr.corp.intel.com>
Date:	Thu, 4 Mar 2010 10:00:17 +0800
From:	"Zhu, Yi" <yi.zhu@...el.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Sridhar Samudrala <sri@...ibm.com>
Subject: RE: [PATCH V2 5/7] sctp: use limited socket backlog

Vlad Yasevich <vladislav.yasevich@...com> wrote:

>> BTW, does the current backlog limit (sysctl_rmem_default[1] << 1) enough for sctp?
>> I noticed the sysctl_sctp_rmem[1] is set to 373500 in my box.
>> 

> sctp uses the same algorithm as TCP to figure out the memory values.
> I guess the issue with using the smaller value that it would be possible to
> queue more the socket receive buffer then to the backlog.  Thus backlog would
> start dropping packets even though receive buffer would still accept them.

Sysctl_tcp_rmem[1] = 87380 in my box which is much smaller than sctp. The backlog
limit is set to 258048 by default which is smaller than sysctl_sctp_rmem[1] = 373500.
I don't think backlog starts to drop packets before receive queue is correct. Fortunately
we can set the limit by individual protocols. I'll set the sk->sk_backlog.limit to
sysctl_sctp_rmem[1] in sctp_init_sock() for sctp socks in the next version.

Thanks,
-yi
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