Hi Edward,

Edward Cree wrote 10.10.2019 21:16:
On 10/10/2019 15:42, Alexander Lobakin wrote:
Commit 323ebb61e32b ("net: use listified RX for handling GRO_NORMAL
skbs") have introduced a sysctl variable gro_normal_batch for defining
a limit for listified Rx of GRO_NORMAL skbs. The initial value of 8 is
purely arbitrary and has been chosen, I believe, as a minimal safe
8 was chosen by performance tests on my setup with v1 of that patch;
 see https://www.spinics.net/lists/netdev/msg585001.html .
Sorry for not including that info in the final version of the patch.
While I didn't re-do tests on varying gro_normal_batch on the final
 version, I think changing it needs more evidence than just "we tested
 it; it's better".  In particular, increasing the batch size should be
 accompanied by demonstration that latency isn't increased in e.g. a
 multi-stream ping-pong test.

However, several tests show that it's rather suboptimal and doesn't
allow to take a full advantage of listified processing. The best and
the most balanced results have been achieved with a batches of 16 skbs
per flush.
So double the default value to give a yet another boost for Rx path.

It remains configurable via sysctl anyway, so may be fine-tuned for
each hardware.
I see this as a reason to leave the default as it is; the combination
 of your tests and mine have established that the optimal size does
 vary (I found 16 to be 2% slower than 8 with my setup), so any
 tweaking of the default is likely only worthwhile if we have data
 over lots of different hardware combinations.

Agree, if you've got slower results on 16, we must leave the default
value, as it seems to be VERY hardware- and driver- dependent.
So, patch 2/2 is not actual any more (I supposed that it would likely
go away before sending this series).

Signed-off-by: Alexander Lobakin <aloba...@dlink.ru>
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index a33f56b439ce..4f60444bb766 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4189,7 +4189,7 @@ int dev_weight_tx_bias __read_mostly = 1; /* bias for output_queue quota */
 int dev_rx_weight __read_mostly = 64;
 int dev_tx_weight __read_mostly = 64;
 /* Maximum number of GRO_NORMAL skbs to batch up for list-RX */
-int gro_normal_batch __read_mostly = 8;
+int gro_normal_batch __read_mostly = 16;

 /* Called with irq disabled */
 static inline void ____napi_schedule(struct softnet_data *sd,

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