netdev - [PATCH net-next 4/4] qed: put cond_resched() in qed_dmae_operation

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Message-ID: <20240930201307.330692-5-mschmidt@redhat.com>
Date: Mon, 30 Sep 2024 22:13:07 +0200
From: Michal Schmidt <mschmidt@...hat.com>
To: Manish Chopra <manishc@...vell.com>,
	netdev@...r.kernel.org
Cc: Caleb Sander <csander@...estorage.com>,
	Alok Prasad <palok@...vell.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next 4/4] qed: put cond_resched() in qed_dmae_operation_wait()

It is OK to sleep in qed_dmae_operation_wait, because it is called only
in process context, while holding p_hwfn->dmae_info.mutex from one of
the qed_dmae_{host,grc}2{host,grc} functions.
The udelay(DMAE_MIN_WAIT_TIME=2) in the function is too short to replace
with usleep_range, but at least it's a suitable point for checking if we
should give up the CPU with cond_resched().

This lowers the latency caused by 'ethtool -d' from 10 ms to less than
2 ms on my test system with voluntary preemption.

Signed-off-by: Michal Schmidt <mschmidt@...hat.com>
---
 drivers/net/ethernet/qlogic/qed/qed_hw.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/qlogic/qed/qed_hw.c b/drivers/net/ethernet/qlogic/qed/qed_hw.c
index 6263f847b6b9..9e5f0dbc8a07 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_hw.c
+++ b/drivers/net/ethernet/qlogic/qed/qed_hw.c
@@ -596,6 +596,7 @@ static int qed_dmae_operation_wait(struct qed_hwfn *p_hwfn)
 	barrier();
 	while (*p_hwfn->dmae_info.p_completion_word != DMAE_COMPLETION_VAL) {
 		udelay(DMAE_MIN_WAIT_TIME);
+		cond_resched();
 		if (++wait_cnt > wait_cnt_limit) {
 			DP_NOTICE(p_hwfn->cdev,
 				  "Timed-out waiting for operation to complete. Completion word is 0x%08x expected 0x%08x.\n",
-- 
2.46.2