netdev - Re: Packet drops observed @ LINUX_MIB

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1393523649.26794.22.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 27 Feb 2014 09:54:09 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sharat Masetty <sharat04@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Packet drops observed @ LINUX_MIB_TCPBACKLOGDROP

On Wed, 2014-02-26 at 19:00 -0700, Sharat Masetty wrote:
> Hi,
> 
> We are trying to achieve category 4 data rates on an ARM device. We
> see that with an incoming TCP stream(IP packets coming in and acks
> going out) lots of packets are getting dropped when the backlog queue
> is full. This is impacting overall data TCP throughput. I am trying to
> understand the full context of why this queue is getting full so
> often.
> 
> From my brief look at the code, it looks to me like the user space
> process is slow and busy in pulling the data from the socket buffer,
> therefore the TCP stack is using this backlog queue in the mean time.
> This queue is also charged against the main socket buffer allocation.
> 
> Can you please explain this backlog queue, and possibly confirm if my
> understanding this  matter is accurate?
> Also can you suggest any ideas on how to mitigate these drops?

You forgot to tell us things like :

1) Kernel version
2) Network driver in use.

Some drivers allocate huge buffers to store incoming frames.

Unfortunately we have to avoid OOM issues in the kernel, so such drivers
are likely to have some skb dropped by the backlog.



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html