serious networking (em) performance (ggate and NFS) problem

Shunsuke SHINOMIYA shino at
Thu Nov 18 19:02:10 PST 2004

 Hi list,
if you suppose your computer has sufficient performance, please try to
disable or adjust parameters of Interrupt Moderation of em.
 In my router(Xeon 2.4GHz and on-board two em interfaces) case, it
improves a router's packet forwarding performance. I think the
interrupt delay by Interrupt Moderation caused NIF's input buffer
overflow or output buffer underrun in this case.

 In order to disable Interrupt Moderation, modify src/sys/dev/em/if_em.c
like the following patch and set hw.em.{rx,tx}_{,abs_}int_delay zero by

 *** if_em.c-       Fri Nov 19 11:22:48 2004
--- if_em.c     Fri Nov 19 11:23:39 2004
*************** em_initialize_receive_unit(struct adapte
*** 2611,2618 ****
--- 2611,2622 ----

                  /* Set the interrupt throttling rate.  Value is calculated
                   * as DEFAULT_ITR = 1/(MAX_INTS_PER_SEC * 256ns) */
+ #if 1
+ #define DEFAULT_ITR             0
+ #else
  #define MAX_INTS_PER_SEC        8000
  #define DEFAULT_ITR             1000000000/(MAX_INTS_PER_SEC * 256)
+ #endif
                  E1000_WRITE_REG(&adapter->hw, ITR, DEFAULT_ITR);

Shunsuke SHINOMIYA <shino at>

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