Messages in this thread | | | Date | Thu, 03 Dec 2009 15:40:41 -0600 | From | "Chris Friesen" <> | Subject | Re: seeing strange values for tcp sk_rmem_alloc |
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On 12/03/2009 11:04 AM, Eric Dumazet wrote: > Chris Friesen a écrit :
>> 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.
> > 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.
Looks like this is indeed the case, changing the loopback mtu to 8K makes it increase in 8K increments. This is quite unexpected, since for UDP it only increases by the actual amount of the data being sent rather than the size of the full MTU.
As it stands, it looks like sk_rmem_alloc isn't very useful. Can you point me to something that is more reflective of the actual space used by the tcp socket? I'd like something that increases monotonically with received data and once it exceeds the configured size then the tcp stack will start dropping packets. Does such a thing exist, or is the tcp stack just too complicated to easily obtain this sort of information?
Thanks for your help,
Chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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