linux-kernel - [PATCH 4.14 148/222] PCI: vmd: White list for fast interrupt handlers

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Date:   Sun, 11 Nov 2018 14:24:05 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Keith Busch <keith.busch@...el.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Jon Derrick:" <jonathan.derrick@...el.com>,
        "Heitke, Kenneth" <kenneth.heitke@...el.com>
Subject: [PATCH 4.14 148/222] PCI: vmd: White list for fast interrupt handlers

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Keith Busch <keith.busch@...el.com>

commit a7f58b9ecfd3c0f63703ec10f4a592cc38dbd1b8 upstream.

Devices with slow interrupt handlers are significantly harming
performance when their interrupt vector is shared with a fast device.

Create a class code white list for devices with known fast interrupt
handlers and let all other devices share a single vector so that they
don't interfere with performance.

At the moment, only the NVM Express class code is on the list, but more
may be added if VMD users desire to use other low-latency devices in
these domains.

Signed-off-by: Keith Busch <keith.busch@...el.com>
[lorenzo.pieralisi@....com: changelog]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Acked-by: Jon Derrick: <jonathan.derrick@...el.com>
Cc: "Heitke, Kenneth" <kenneth.heitke@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/pci/host/vmd.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/drivers/pci/host/vmd.c
+++ b/drivers/pci/host/vmd.c
@@ -183,9 +183,20 @@ static struct vmd_irq_list *vmd_next_irq
 	int i, best = 1;
 	unsigned long flags;
 
-	if (pci_is_bridge(msi_desc_to_pci_dev(desc)) || vmd->msix_count == 1)
+	if (vmd->msix_count == 1)
 		return &vmd->irqs[0];
 
+	/*
+	 * White list for fast-interrupt handlers. All others will share the
+	 * "slow" interrupt vector.
+	 */
+	switch (msi_desc_to_pci_dev(desc)->class) {
+	case PCI_CLASS_STORAGE_EXPRESS:
+		break;
+	default:
+		return &vmd->irqs[0];
+	}
+
 	raw_spin_lock_irqsave(&list_lock, flags);
 	for (i = 1; i < vmd->msix_count; i++)
 		if (vmd->irqs[i].count < vmd->irqs[best].count)