On Mon, Jan 24, 2011 at 11:01:45AM -0800, Rick Jones wrote:

Michael S. Tsirkin wrote:

quoted

On Mon, Jan 24, 2011 at 10:27:55AM -0800, Rick Jones wrote:

quoted

quoted

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))

Pity - seems to work back on 2.6.26:

Hmm, that code is there at least as far back as 2.6.12.

raj@tardy:~/netperf2_trunk$ src/netperf -t UDP_STREAM -- -S 1 -m 1024
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
localhost (127.0.0.1) port 0 AF_INET : histogram
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

124928    1024   10.00     2882334      0    2361.17
   256           10.00           0              0.00

raj@tardy:~/netperf2_trunk$ uname -a
Linux tardy 2.6.26-2-amd64 #1 SMP Sun Jun 20 20:16:30 UTC 2010 x86_64 GNU/Linux

Still, even with that (or SIGSTOP) we don't really know where the
packets were dropped right?  There is no guarantee they weren't
dropped before they got to the socket buffer

happy benchmarking,
rick jones

Right. Better send to a port with no socket listening there,
that would drop the packet at an early (if not at the earliest
possible)  opportunity.

PS - here is with a -S 1024 option:

raj@tardy:~/netperf2_trunk$ src/netperf -t UDP_STREAM -- -S 1024 -m 1024
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
localhost (127.0.0.1) port 0 AF_INET : histogram
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

124928    1024   10.00     1679269      0    1375.64
  2048           10.00     1490662           1221.13

showing that there is a decent chance that many of the frames were
dropped at the socket buffer, but not all - I suppose I could/should
be checking netstat stats... :)

And just a little more, only because I was curious :)

raj@tardy:~/netperf2_trunk$ src/netperf -t UDP_STREAM -- -S 1M -m 257
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
localhost (127.0.0.1) port 0 AF_INET : histogram
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

124928     257   10.00     1869134      0     384.29
262142           10.00     1869134            384.29

raj@tardy:~/netperf2_trunk$ src/netperf -t UDP_STREAM -- -S 1 -m 257
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
localhost (127.0.0.1) port 0 AF_INET : histogram
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

124928     257   10.00     3076363      0     632.49
   256           10.00           0              0.00