netdev - Re: [PATCH v1 3/3] usb: gadget: NCM: Stop RX TCP Bursts getting dropped.

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Date:	Fri, 30 May 2014 12:25:48 +0100
From:	Jim Baxter <jim_baxter@...tor.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Bjørn Mork <bjorn@...k.no>,
	David Laight <David.Laight@...LAB.COM>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH v1 3/3] usb: gadget: NCM: Stop RX TCP Bursts getting dropped.

On 29/05/14 20:04, Eric Dumazet wrote:
> On Thu, 2014-05-29 at 18:12 +0100, Jim Baxter wrote:
>> This fixes a problem with dropped packets over 16k CDC-NCM
>> when the connection is being heavily used.
>>
>> The issue was that the skb truesize for the unpacked NCM
>> packets was too high after they were cloned from the 16k
>> skb, this lead to the potential memory calculated by the
>> Kernel running out of memory earlier then it should.
>>
>> Signed-off-by: Jim Baxter <jim_baxter@...tor.com>
>> ---
> 
> Note the patch is OK, but changelog a bit misleading ;)
> 
> Kernel was not running out of memory, because truesize was correct.
> 
> The problem here is that a frame was consuming more kernel memory than
> really needed, so chances of hitting socket sk_rcvbuf limit was high.
> 
> BTW :
> #define NTB_OUT_SIZE              16384
> 
> alloc_skb(size) ->
> 	kmalloc(16384 + sizeof(struct skb_shared_info)) ->
> 		roundup() => 32768
> 
> So truesize of the skb was infact ~32KB, which is really insane indeed.
> After your patch, its back to ~2KB
> 
> Acked-by: Eric Dumazet <edumazet@...gle.com>
> 
> 
> 

Thank you, I will clarify the description.

Jim

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