From: Halil Pasic <pasic@xxxxxxxxxxxxx> The current value of SMC_WR_BUF_CNT is 16 which leads to heavy contention on the wr_tx_wait workqueue of the SMC-R linkgroup and its spinlock when many connections are competing for the buffer. Currently up to 256 connections per linkgroup are supported. To make things worse when finally a buffer becomes available and smc_wr_tx_put_slot() signals the linkgroup's wr_tx_wait wq, because WQ_FLAG_EXCLUSIVE is not used all the waiters get woken up, most of the time a single one can proceed, and the rest is contending on the spinlock of the wq to go to sleep again. For some reason include/linux/wait.h does not offer a top level wrapper macro for wait_event with interruptible, exclusive and timeout. I did not spend too many cycles on thinking if that is even a combination that makes sense (on the quick I don't see why not) and conversely I refrained from making an attempt to accomplish the interruptible, exclusive and timeout combo by using the abstraction-wise lower level __wait_event interface. To alleviate the tx performance bottleneck and the CPU overhead due to the spinlock contention, let us increase SMC_WR_BUF_CNT to 256. Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx> Reported-by: Nils Hoppmann <niho@xxxxxxxxxxxxx> Reviewed-by: Wenjia Zhang <wenjia@xxxxxxxxxxxxx> Signed-off-by: Wenjia Zhang <wenjia@xxxxxxxxxxxxx> --- net/smc/smc_wr.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/smc/smc_wr.h b/net/smc/smc_wr.h index f3008dda222a..81e772e241f3 100644 --- a/net/smc/smc_wr.h +++ b/net/smc/smc_wr.h @@ -19,7 +19,7 @@ #include "smc.h" #include "smc_core.h" -#define SMC_WR_BUF_CNT 16 /* # of ctrl buffers per link */ +#define SMC_WR_BUF_CNT 256 /* # of ctrl buffers per link */ #define SMC_WR_TX_WAIT_FREE_SLOT_TIME (10 * HZ) -- 2.43.0
