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Diffstat (limited to 'Documentation/networking/pktgen.txt')
| -rw-r--r-- | Documentation/networking/pktgen.txt | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/Documentation/networking/pktgen.txt b/Documentation/networking/pktgen.txt index 0e30c7845b2b..0dffc6e37902 100644 --- a/Documentation/networking/pktgen.txt +++ b/Documentation/networking/pktgen.txt @@ -24,6 +24,34 @@ For monitoring and control pktgen creates: /proc/net/pktgen/ethX +Tuning NIC for max performance +============================== + +The default NIC setting are (likely) not tuned for pktgen's artificial +overload type of benchmarking, as this could hurt the normal use-case. + +Specifically increasing the TX ring buffer in the NIC: + # ethtool -G ethX tx 1024 + +A larger TX ring can improve pktgen's performance, while it can hurt +in the general case, 1) because the TX ring buffer might get larger +than the CPUs L1/L2 cache, 2) because it allow more queueing in the +NIC HW layer (which is bad for bufferbloat). + +One should be careful to conclude, that packets/descriptors in the HW +TX ring cause delay. Drivers usually delay cleaning up the +ring-buffers (for various performance reasons), thus packets stalling +the TX ring, might just be waiting for cleanup. + +This cleanup issues is specifically the case, for the driver ixgbe +(Intel 82599 chip). This driver (ixgbe) combine TX+RX ring cleanups, +and the cleanup interval is affected by the ethtool --coalesce setting +of parameter "rx-usecs". + +For ixgbe use e.g "30" resulting in approx 33K interrupts/sec (1/30*10^6): + # ethtool -C ethX rx-usecs 30 + + Viewing threads =============== /proc/net/pktgen/kpktgend_0 |