[dpdk-dev] [PATCH] i40evf: use non spinning delay when issuing AQ request to PF

[Laurent Hardy <laurent.hardy@6wind.com>]

When a port is handled by the i40evf dpdk pmd we could observe a cpu usage
around 70% in case of rte eth stats functions (rte_eth_stats_get and
rte_eth_xstats_get) called periodically via an application control thread.

This is due to the polling mechanism to handle communication between VF
and PF introduced for x710 (eg: VSI and virtual channel).

After issuing any request to the PF, the VF will wait in a blocking mode
until it gets a response from the PF or until timeout (2sec).
Instead, uses rte_delay_us_sleep to sleep for ASQ_DELAY_MS, which will
use system sleep and will not block the CPU core.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Signed-off-by: Laurent Hardy <laurent.hardy@6wind.com>

---
Hi all,
Some question coming along with this patch:
1)Is there any downside to use the rte_eal_delay_us_sleep which will
put the thread to sleep instead of the rte_eal_delay_ms (for both
control plane and dataplane threads) ?

2)Another alternative to this patch could be to modify at librte_eal
layer the function rte_eal_delay to put the thread to sleep in case of
application control plane thread (by looking at the coreid).

    --- a/lib/librte_eal/common/include/generic/rte_cycles.h
    +++ b/lib/librte_eal/common/include/generic/rte_cycles.h
    @@ -13,9 +13,11 @@
    */

     #include <stdint.h>
    +#include <unistd.h>
     #include <rte_compat.h>
     #include <rte_debug.h>
     #include <rte_atomic.h>
    +#include <rte_lcore.h>

     #define MS_PER_S 1000
     #define US_PER_S 1000000
    @@ -147,7 +149,10 @@ extern void
     static inline void
     rte_delay_ms(unsigned ms)
     {
    -	rte_delay_us(ms * 1000);
    +	if (rte_lcore_id() == LCORE_ID_ANY)
    +		usleep(ms * 1000);
    +	else
    +		rte_delay_us(ms * 1000);
     }

regards,
Laurent
---
 drivers/net/i40e/i40e_ethdev_vf.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/i40e/i40e_ethdev_vf.c b/drivers/net/i40e/i40e_ethdev_vf.c
index 244397e0e..c700c66fd 100644
--- a/drivers/net/i40e/i40e_ethdev_vf.c
+++ b/drivers/net/i40e/i40e_ethdev_vf.c
@@ -315,6 +315,7 @@ _atomic_set_cmd(struct i40e_vf *vf, enum virtchnl_ops ops)
 
 #define MAX_TRY_TIMES 200
 #define ASQ_DELAY_MS  10
+#define DELAY_MS(x) DELAY(x * 1000)
 
 static int
 i40evf_execute_vf_cmd(struct rte_eth_dev *dev, struct vf_cmd_info *args)
@@ -358,7 +359,7 @@ i40evf_execute_vf_cmd(struct rte_eth_dev *dev, struct vf_cmd_info *args)
 				break;
 			} else if (ret == I40EVF_MSG_ERR)
 				break;
-			rte_delay_ms(ASQ_DELAY_MS);
+			DELAY_MS(ASQ_DELAY_MS);
 			/* If don't read msg or read sys event, continue */
 		} while (i++ < MAX_TRY_TIMES);
 		_clear_cmd(vf);
@@ -380,7 +381,7 @@ i40evf_execute_vf_cmd(struct rte_eth_dev *dev, struct vf_cmd_info *args)
 					   ret == I40EVF_MSG_CMD) {
 				break;
 			}
-			rte_delay_ms(ASQ_DELAY_MS);
+			DELAY_MS(ASQ_DELAY_MS);
 			/* If don't read msg or read sys event, continue */
 		} while (i++ < MAX_TRY_TIMES);
 		_clear_cmd(vf);
@@ -394,7 +395,7 @@ i40evf_execute_vf_cmd(struct rte_eth_dev *dev, struct vf_cmd_info *args)
 				err = 0;
 				break;
 			}
-			rte_delay_ms(ASQ_DELAY_MS);
+			DELAY_MS(ASQ_DELAY_MS);
 			/* If don't read msg or read sys event, continue */
 		} while (i++ < MAX_TRY_TIMES);
 		/* If there's no response is received, clear command */
-- 
2.24.1