linux-kernel - [PATCH 4.19 19/50] ixgbe: Prevent u8 wrapping of ITR value to something less than 10us

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Message-Id: <20190918061225.140090286@linuxfoundation.org>
Date:   Wed, 18 Sep 2019 08:19:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Gregg Leventhal <gleventhal@...estreet.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Andrew Bowers <andrewx.bowers@...el.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [PATCH 4.19 19/50] ixgbe: Prevent u8 wrapping of ITR value to something less than 10us

From: Alexander Duyck <alexander.h.duyck@...ux.intel.com>

commit 377228accbbb8b9738f615d791aa803f41c067e0 upstream.

There were a couple cases where the ITR value generated via the adaptive
ITR scheme could exceed 126. This resulted in the value becoming either 0
or something less than 10. Switching back and forth between a value less
than 10 and a value greater than 10 can cause issues as certain hardware
features such as RSC to not function well when the ITR value has dropped
that low.

CC: stable@...r.kernel.org
Fixes: b4ded8327fea ("ixgbe: Update adaptive ITR algorithm")
Reported-by: Gregg Leventhal <gleventhal@...estreet.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2626,7 +2626,7 @@ adjust_by_size:
 		/* 16K ints/sec to 9.2K ints/sec */
 		avg_wire_size *= 15;
 		avg_wire_size += 11452;
-	} else if (avg_wire_size <= 1980) {
+	} else if (avg_wire_size < 1968) {
 		/* 9.2K ints/sec to 8K ints/sec */
 		avg_wire_size *= 5;
 		avg_wire_size += 22420;
@@ -2659,6 +2659,8 @@ adjust_by_size:
 	case IXGBE_LINK_SPEED_2_5GB_FULL:
 	case IXGBE_LINK_SPEED_1GB_FULL:
 	case IXGBE_LINK_SPEED_10_FULL:
+		if (avg_wire_size > 8064)
+			avg_wire_size = 8064;
 		itr += DIV_ROUND_UP(avg_wire_size,
 				    IXGBE_ITR_ADAPTIVE_MIN_INC * 64) *
 		       IXGBE_ITR_ADAPTIVE_MIN_INC;