Re: [PATCH 1/5] net: mvneta: increase the 64-bit rx/tx stats out of the hot path

On Sun, Jan 12, 2014 at 04:49:52PM -0800, Eric Dumazet wrote:

On Sun, 2014-01-12 at 10:31 +0100, Willy Tarreau wrote:

quoted

Better count packets and bytes in the stack and on 32 bit then
accumulate them at the end for once. This saves two memory writes
and two memory barriers per packet. The incoming packet rate was
increased by 4.7% on the Openblocks AX3 thanks to this.

Cc: Thomas Petazzoni <redacted>
Cc: Gregory CLEMENT <redacted>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 drivers/net/ethernet/marvell/mvneta.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

Reviewed-by: Eric Dumazet <edumazet@google.com>

Note that with such a cost, one has to wonder why we keep 64bit stats
for this NIC on 32bit hosts...

At least this avoids wrapping if stats are not retrieved often enough.
As someone who had to support 32-bit stats in production on a firewall
running on kernel 2.4, I can say it really becomes a problem to graph
activity if stats are not collected as often as every 30 seconds, which
is short in certain environments.

Thanks,
Willy