linux-kernel - [PATCH] msi: skip calling pci_find_capability from msi_set_mask

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Message-ID: <48310691.9050706@jp.fujitsu.com>
Date:	Mon, 19 May 2008 13:48:17 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
CC:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: [PATCH] msi: skip calling pci_find_capability from msi_set_mask_bits

Jesse Barnes wrote:
> Since we know MSI is a problem, let's just go with fixing that for now.  If we 
> find that other caps are also causing problems we can revisit caching all of 
> them; the patch is simple enough.

Humm...
I suppose it can be more simple. How about this patch?


> everytime handle_edge_irq is called it needs to mask and unmask MSI, and
> that leads to a series of very expensive calls to pci_find_capability

The position of MSI capability is already cached in the msi_desc when
we enter the msi_set_mask_bits().  Use it instead.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
---
 drivers/pci/msi.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 8c61304..ccb1974 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -70,12 +70,10 @@ arch_teardown_msi_irqs(struct pci_dev *dev)
 	}
 }
 
-static void msi_set_enable(struct pci_dev *dev, int enable)
+static void __msi_set_enable(struct pci_dev *dev, int pos, int enable)
 {
-	int pos;
 	u16 control;
 
-	pos = pci_find_capability(dev, PCI_CAP_ID_MSI);
 	if (pos) {
 		pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &control);
 		control &= ~PCI_MSI_FLAGS_ENABLE;
@@ -85,6 +83,11 @@ static void msi_set_enable(struct pci_dev *dev, int enable)
 	}
 }
 
+static void msi_set_enable(struct pci_dev *dev, int enable)
+{
+	__msi_set_enable(dev, pci_find_capability(dev, PCI_CAP_ID_MSI), enable);
+}
+
 static void msix_set_enable(struct pci_dev *dev, int enable)
 {
 	int pos;
@@ -141,7 +144,8 @@ static void msi_set_mask_bits(unsigned int irq, u32 mask, u32 flag)
 			mask_bits |= flag & mask;
 			pci_write_config_dword(entry->dev, pos, mask_bits);
 		} else {
-			msi_set_enable(entry->dev, !flag);
+			__msi_set_enable(entry->dev, entry->msi_attrib.pos,
+					 !flag);
 		}
 		break;
 	case PCI_CAP_ID_MSIX:
-- 
1.5.4.3

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