Re: [PATCH] qed: avoid spin loops in _qed_mcp_cmd_and_union()
From: Eric Dumazet <hidden>
Date: 2021-10-27 22:25:35
On 10/27/21 2:45 PM, Caleb Sander wrote:
quoted hunk ↗ jump to hunk
By default, qed_mcp_cmd_and_union() sets max_retries to 500K and usecs to 10, so these loops can together delay up to 5s. We observed thread scheduling delays of over 700ms in production, with stacktraces pointing to this code as the culprit. Add calls to cond_resched() in both loops to yield the CPU if necessary. Signed-off-by: Caleb Sander <redacted> Reviewed-by: Joern Engel <redacted> --- drivers/net/ethernet/qlogic/qed/qed_mcp.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)diff --git a/drivers/net/ethernet/qlogic/qed/qed_mcp.c b/drivers/net/ethernet/qlogic/qed/qed_mcp.c index 24cd41567..d6944f020 100644 --- a/drivers/net/ethernet/qlogic/qed/qed_mcp.c +++ b/drivers/net/ethernet/qlogic/qed/qed_mcp.c@@ -485,10 +485,12 @@ _qed_mcp_cmd_and_union(struct qed_hwfn *p_hwfn, spin_unlock_bh(&p_hwfn->mcp_info->cmd_lock); - if (QED_MB_FLAGS_IS_SET(p_mb_params, CAN_SLEEP)) + if (QED_MB_FLAGS_IS_SET(p_mb_params, CAN_SLEEP)) {
I do not know this driver, but apparently, there is this CAN_SLEEP test hinting about being able to sleep.
msleep(msecs);
- else
+ } else {
+ cond_resched();Here you might sleep/schedule, while CAN_SLEEP was not set ?
udelay(usecs);
I would suggest using usleep_range() instead, because cond_resched() can be a NOP under some circumstances.
+ } } while (++cnt < max_retries);
Then perhaps not count against max_retries, but based on total elapsed time ?
quoted hunk ↗ jump to hunk
if (cnt >= max_retries) {@@ -517,10 +519,12 @@ _qed_mcp_cmd_and_union(struct qed_hwfn *p_hwfn, * The spinlock stays locked until the list element is removed. */ - if (QED_MB_FLAGS_IS_SET(p_mb_params, CAN_SLEEP)) + if (QED_MB_FLAGS_IS_SET(p_mb_params, CAN_SLEEP)) { msleep(msecs); - else + } else { + cond_resched(); udelay(usecs); + } spin_lock_bh(&p_hwfn->mcp_info->cmd_lock);