linux-kernel - [PATCH] VFIO: PCI: eliminate unnecessary overhead in vfio_pci_reflck

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Date:   Wed, 30 Oct 2019 18:57:10 +0800
From:   linmiaohe <linmiaohe@...wei.com>
To:     <alex.williamson@...hat.com>, <cohuck@...hat.com>,
        <eric.auger@...hat.com>, <aik@...abs.ru>, <mpe@...erman.id.au>,
        <bhelgaas@...gle.com>, <tglx@...utronix.de>, <hexin.op@...il.com>
CC:     <linmiaohe@...wei.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] VFIO: PCI: eliminate unnecessary overhead in vfio_pci_reflck_find

From: Miaohe Lin <linmiaohe@...wei.com>

The driver of the pci device may not equal to vfio_pci_driver,
but we fetch vfio_device from pci_dev unconditionally in func
vfio_pci_reflck_find. This overhead, such as the competition
of vfio.group_lock, can be eliminated by check pci_dev_driver
with vfio_pci_driver first.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 drivers/vfio/pci/vfio_pci.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 379a02c36e37..1e21970543a6 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1466,15 +1466,14 @@ static int vfio_pci_reflck_find(struct pci_dev *pdev, void *data)
 	struct vfio_device *device;
 	struct vfio_pci_device *vdev;
 
-	device = vfio_device_get_from_dev(&pdev->dev);
-	if (!device)
-		return 0;
-
 	if (pci_dev_driver(pdev) != &vfio_pci_driver) {
-		vfio_device_put(device);
 		return 0;
 	}
 
+	device = vfio_device_get_from_dev(&pdev->dev);
+	if (!device)
+		return 0;
+
 	vdev = vfio_device_data(device);
 
 	if (vdev->reflck) {
-- 
2.19.1