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From:   korantwork@gmail.com
To:     nirmal.patel@linux.intel.com, jonathan.derrick@linux.dev,
        lpieralisi@kernel.org
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xinghui Li <korantli@tencent.com>
Subject: [PATCH] PCI: vmd: Do not disable MSI-X remapping in VMD 28C0 controller
Date:   Thu, 22 Dec 2022 15:26:03 +0800
Message-Id: <20221222072603.1175248-1-korantwork@gmail.com>
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From: Xinghui Li <korantli@tencent.com>

Commit ee81ee84f873("PCI: vmd: Disable MSI-X remapping when possible")
disable the vmd MSI-X remapping for optimizing pci performance.However,
this feature severely negatively optimized performance in multi-disk
situations.

In FIO 4K random test, we test 1 disk in the 1 CPU

when disable MSI-X remapping:
read: IOPS=1183k, BW=4622MiB/s (4847MB/s)(1354GiB/300001msec)
READ: bw=4622MiB/s (4847MB/s), 4622MiB/s-4622MiB/s (4847MB/s-4847MB/s),
io=1354GiB (1454GB), run=300001-300001msec

When not disable MSI-X remapping:
read: IOPS=1171k, BW=4572MiB/s (4795MB/s)(1340GiB/300001msec)
READ: bw=4572MiB/s (4795MB/s), 4572MiB/s-4572MiB/s (4795MB/s-4795MB/s),
io=1340GiB (1438GB), run=300001-300001msec

However, the bypass mode could increase the interrupts costs in CPU.
We test 12 disks in the 6 CPU,

When disable MSI-X remapping:
read: IOPS=562k, BW=2197MiB/s (2304MB/s)(644GiB/300001msec)
READ: bw=2197MiB/s (2304MB/s), 2197MiB/s-2197MiB/s (2304MB/s-2304MB/s),
io=644GiB (691GB), run=300001-300001msec

When not disable MSI-X remapping:
read: IOPS=1144k, BW=4470MiB/s (4687MB/s)(1310GiB/300005msec)
READ: bw=4470MiB/s (4687MB/s), 4470MiB/s-4470MiB/s (4687MB/s-4687MB/s),
io=1310GiB (1406GB), run=300005-300005msec

Signed-off-by: Xinghui Li <korantli@tencent.com>
---
 drivers/pci/controller/vmd.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index e06e9f4fc50f..9f6e9324d67d 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -998,8 +998,7 @@ static const struct pci_device_id vmd_ids[] = {
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP,},
 	{PCI_DEVICE(PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_VMD_28C0),
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW |
-				VMD_FEAT_HAS_BUS_RESTRICTIONS |
-				VMD_FEAT_CAN_BYPASS_MSI_REMAP,},
+				VMD_FEAT_HAS_BUS_RESTRICTIONS,},
 	{PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x467f),
 		.driver_data = VMD_FEAT_HAS_MEMBAR_SHADOW_VSCAP |
 				VMD_FEAT_HAS_BUS_RESTRICTIONS |
-- 
2.39.0