linux/drivers/net/bonding
Tom Herbert c6e1a0d12c net: Allow no-cache copy from user on transmit
This patch uses __copy_from_user_nocache on transmit to bypass data
cache for a performance improvement.  skb_add_data_nocache and
skb_copy_to_page_nocache can be called by sendmsg functions to use
this feature, initial support is in tcp_sendmsg.  This functionality is
configurable per device using ethtool.

Presumably, this feature would only be useful when the driver does
not touch the data.  The feature is turned on by default if a device
indicates that it does some form of checksum offload; it is off by
default for devices that do no checksum offload or indicate no checksum
is necessary.  For the former case copy-checksum is probably done
anyway, in the latter case the device is likely loopback in which case
the no cache copy is probably not beneficial.

This patch was tested using 200 instances of netperf TCP_RR with
1400 byte request and one byte reply.  Platform is 16 core AMD x86.

No-cache copy disabled:
   672703 tps, 97.13% utilization
   50/90/99% latency:244.31 484.205 1028.41

No-cache copy enabled:
   702113 tps, 96.16% utilization,
   50/90/99% latency 238.56 467.56 956.955

Using 14000 byte request and response sizes demonstrate the
effects more dramatically:

No-cache copy disabled:
   79571 tps, 34.34 %utlization
   50/90/95% latency 1584.46 2319.59 5001.76

No-cache copy enabled:
   83856 tps, 34.81% utilization
   50/90/95% latency 2508.42 2622.62 2735.88

Note especially the effect on latency tail (95th percentile).

This seems to provide a nice performance improvement and is
consistent in the tests I ran.  Presumably, this would provide
the greatest benfits in the presence of an application workload
stressing the cache and a lot of transmit data happening.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2011-04-04 22:30:30 -07:00
..
bond_3ad.c bonding: wrap slave state work 2011-03-16 12:51:20 -07:00
bond_3ad.h bonding 802.3ad: Rename rx_machine_lock to state_machine_lock 2011-03-07 16:02:18 -08:00
bond_alb.c bonding: use the correct size for _simple_hash() 2011-02-28 13:21:28 -08:00
bond_alb.h bonding:typo in comment 2011-03-31 01:54:22 -07:00
bond_debugfs.c bonding: add the debugfs interface to see RLB hash table 2010-12-16 13:16:05 -08:00
bond_ipv6.c bonding/vlan: Fix mangled NAs on slaves without VLAN tag insertion 2010-12-16 12:43:22 -08:00
bond_main.c net: Allow no-cache copy from user on transmit 2011-04-04 22:30:30 -07:00
bond_procfs.c bonding: move procfs code into bond_procfs.c 2011-03-09 13:32:17 -08:00
bond_sysfs.c bonding: get rid of IFF_SLAVE_INACTIVE netdev->priv_flag 2011-03-16 12:51:20 -07:00
bonding.h bonding: fix rx_handler locking 2011-03-23 12:45:10 -07:00
Makefile bonding: move procfs code into bond_procfs.c 2011-03-09 13:32:17 -08:00