Messages in this thread | | | Date | Fri, 11 Oct 2019 10:23:37 +0300 | From | Alexander Lobakin <> | Subject | Re: [PATCH net-next 2/2] net: core: increase the default size of GRO_NORMAL skb lists to flush |
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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 >> default. > 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 <alobakin@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,
Regards, ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
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