On Mon, Jan 24, 2011 at 10:27:55AM -0800, Rick Jones wrote:
> >
> >Just to block netperf you can send it SIGSTOP :)
> >
>
> Clever :) One could I suppose achieve the same result by making the
> remote receive socket buffer size smaller than the UDP message size
> and then not worry about having to learn the netserver's PID to send
> it the SIGSTOP. I *think* the semantics will be substantially the
> same?
If you could set, it, yes. But at least linux ignores
any value substantially smaller than 1K, and then
multiplies that by 2:
case SO_RCVBUF:
/* Don't error on this BSD doesn't and if you think
about it this is right. Otherwise apps have to
play 'guess the biggest size' games. RCVBUF/SNDBUF
are treated in BSD as hints */
if (val > sysctl_rmem_max)
val = sysctl_rmem_max;
set_rcvbuf:
sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
/*
* We double it on the way in to account for
* "struct sk_buff" etc. overhead. Applications
* assume that the SO_RCVBUF setting they make will
* allow that much actual data to be received on that
* socket.
*
* Applications are unaware that "struct sk_buff" and
* other overheads allocate from the receive buffer
* during socket buffer allocation.
*
* And after considering the possible alternatives,
* returning the value we actually used in getsockopt
* is the most desirable behavior.
*/
if ((val * 2) < SOCK_MIN_RCVBUF)
sk->sk_rcvbuf = SOCK_MIN_RCVBUF;
else
sk->sk_rcvbuf = val * 2;
and
/*
* Since sk_rmem_alloc sums skb->truesize, even a small frame might need
* sizeof(sk_buff) + MTU + padding, unless net driver perform copybreak
*/
#define SOCK_MIN_RCVBUF (2048 + sizeof(struct sk_buff))
> Both will be drops at the socket buffer, albeit for for
> different reasons. The "too small socket buffer" version though
> doesn't require one remember to "wake" the netserver in time to have
> it send results back to netperf without netperf tossing-up an error
> and not reporting any statistics.
>
> Also, netperf has a "no control connection" mode where you can, in
> effect cause it to send UDP datagrams out into the void - I put it
> there to allow folks to test against the likes of echo discard and
> chargen services but it may have a use here. Requires that one
> specify the destination IP and port for the "data connection"
> explicitly via the test-specific options. In that mode the only
> stats reported are those local to netperf rather than netserver.
Ah, sounds perfect.
> happy benchmarking,
>
> rick jones
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