Re: [PATCH] Increase nptl test case buffer size so we really block on current Linux kernels.

[Andreas Jaeger <aj at suse dot com>]

On 07/23/2013 10:40 AM, David Miller wrote:
> From: Andreas Jaeger <aj@suse.com>
> Date: Tue, 23 Jul 2013 06:54:22 +0200
> 
>> Since this hit us, could you document the reason for the buffer size?
> 
> Sure, how does this look?

Fine to me, thanks,
Andreas

> --------------------
> Increase nptl test case buffer size so we really block on current Linux kernels.
> 
> 	* tst-cancel4.c (WRITE_BUFFER_SIZE): Increase to 16384.
> 
> diff --git a/nptl/ChangeLog b/nptl/ChangeLog
> index fc2ef41..0e4747e 100644
> --- a/nptl/ChangeLog
> +++ b/nptl/ChangeLog
> @@ -1,3 +1,7 @@
> +2013-07-22  David S. Miller  <davem@davemloft.net>
> +
> +	* tst-cancel4.c (WRITE_BUFFER_SIZE): Increase to 16384.
> +
>  2013-07-19  Dominik Vogt  <vogt@de.ibm.com>
>  
>  	* pthread_mutex_lock.c: Fix whitespace.
> diff --git a/nptl/tst-cancel4.c b/nptl/tst-cancel4.c
> index 9ffd5d1..10b7c6e 100644
> --- a/nptl/tst-cancel4.c
> +++ b/nptl/tst-cancel4.c
> @@ -83,7 +83,30 @@ static pthread_barrier_t b2;
>  # define IPC_ADDVAL 0
>  #endif
>  
> -#define WRITE_BUFFER_SIZE 4096
> +/* The WRITE_BUFFER_SIZE value needs to be choosen such that if we set
> +   the socket send buffer size to '1', a write of this size on that
> +   socket will block.
> +
> +   The Linux kernel imposes a minimum send socket buffer size
> +   which has changed over the years.  Currently the value is:
> +
> +     2 * (2048 + SKB_DATA_ALIGN(sizeof(struct sk_buff)))
> +
> +   which is attempting to make sure that with standard MTUs,
> +   TCP can always queue up at least 2 full sized packets.
> +
> +   Furthermore, there is logic in the socket send paths that
> +   will allow one more packet (of any size) to be queued up as
> +   long as some socket buffer space remains.   Blocking only
> +   occurs when we try to queue up a new packet and the send
> +   buffer space has already been fully consumed.
> +
> +   Therefore we must set this value to the largest possible value of
> +   the formula above (and since it depends upon the size of "struct
> +   sk_buff", it is dependent upon machine word size etc.) plus some
> +   slack space.  */
> +
> +#define WRITE_BUFFER_SIZE 16384
>  
>  /* Cleanup handling test.  */
>  static int cl_called;
> 


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 Andreas Jaeger aj@{suse.com,opensuse.org} Twitter/Identica: jaegerandi
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