diff mbox series

[v2] i40e: avoid spin loop in i40e_asq_send_command()

Message ID 20211101173808.1735144-1-csander@purestorage.com (mailing list archive)
State Awaiting Upstream
Delegated to: Netdev Maintainers
Headers show
Series [v2] i40e: avoid spin loop in i40e_asq_send_command() | expand

Checks

Context Check Description
netdev/cover_letter success Single patches do not need cover letters
netdev/fixes_present success Fixes tag not required for -next series
netdev/patch_count success Link
netdev/subject_prefix warning Target tree name not specified in the subject
netdev/cc_maintainers warning 1 maintainers not CCed: jesse.brandeburg@intel.com
netdev/source_inline success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/module_param success Was 0 now: 0
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/verify_fixes success No Fixes tag
netdev/checkpatch warning WARNING: line length of 95 exceeds 80 columns
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/header_inline success No static functions without inline keyword in header files
netdev/tree_selection success Guessing tree name failed - patch did not apply

Commit Message

Caleb Sander Nov. 1, 2021, 5:38 p.m. UTC 
Previously, the kernel could spend up to 250 ms waiting for a command to
be submitted to an admin queue. This function is also called in a loop,
e.g., in i40e_get_module_eeprom() (through i40e_aq_get_phy_register()),
so the time spent in the kernel may be even higher. We observed
scheduling delays of over 2 seconds in production,
with stacktraces pointing to this code as the culprit.

Use usleep_range() instead of udelay() so the loop can yield the CPU.
Also compute the elapsed time using the jiffies counter rather than
assuming udelay() waits exactly the time interval requested.

Signed-off-by: Caleb Sander <csander@purestorage.com>
Reviewed-by: Joern Engel <joern@purestorage.com>
---
 drivers/net/ethernet/intel/i40e/i40e_adminq.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Changed from v1:
Use usleep_range() instead of udelay() + cond_resched(),
to avoid using the CPU while waiting.
Use 50 us as the max for the range since hrtimers schedules the sleep
for the max (unless another timer interrupt occurs after the min).
Since checking if the command is done too frequently would waste time
context-switching, use half of the max (25 us) as the min for the range.
diff mbox series

Patch

diff --git a/drivers/net/ethernet/intel/i40e/i40e_adminq.c b/drivers/net/ethernet/intel/i40e/i40e_adminq.c
index 593912b17..b2c27ab3b 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_adminq.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_adminq.c
@@ -902,7 +902,7 @@  i40e_status i40e_asq_send_command(struct i40e_hw *hw,
 	 * we need to wait for desc write back
 	 */
 	if (!details->async && !details->postpone) {
-		u32 total_delay = 0;
+		unsigned long timeout_end = jiffies + usecs_to_jiffies(hw->aq.asq_cmd_timeout);
 
 		do {
 			/* AQ designers suggest use of head for better
@@ -910,9 +910,8 @@  i40e_status i40e_asq_send_command(struct i40e_hw *hw,
 			 */
 			if (i40e_asq_done(hw))
 				break;
-			udelay(50);
-			total_delay += 50;
-		} while (total_delay < hw->aq.asq_cmd_timeout);
+			usleep_range(25, 50);
+		} while (time_before(jiffies, timeout_end));
 	}
 
 	/* if ready, copy the desc back to temp */