linux-kernel - Re: [PATCH] iommu/vt-d: Ratelimit fault handler

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Date:	Tue, 15 Mar 2016 10:10:51 -0700
From:	Joe Perches <joe@...ches.com>
To:	Alex Williamson <alex.williamson@...hat.com>,
	iommu@...ts.linux-foundation.org, dwmw2@...radead.org
Cc:	joro@...tes.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: Ratelimit fault handler

On Tue, 2016-03-15 at 10:35 -0600, Alex Williamson wrote:
> Fault rates can easily overwhelm the console and make the system
> unresponsive.  Ratelimit to allow an opportunity for maintenance.

A few suggestions:

o Use a single ratelimit state.
o The multiple lines output are unnecessary and hard to grep
  in the dmesg output because of inconsistent prefixing as
  second and subsequent output lines are not prefixed by pr_fmt.
o The DMAR prefix on the second block is also unnecessary as
  it's already prefixed by pr_fmt
o Coalesce the formats for easier grep.

so maybe:
---
 drivers/iommu/dmar.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 8ffd756..59dcaaa 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -1575,23 +1575,27 @@ static int dmar_fault_do_one(struct intel_iommu *iommu, int type,
 {
 	const char *reason;
 	int fault_type;
+	static DEFINE_RATELIMIT_STATE(rs,
+				      DEFAULT_RATELIMIT_INTERVAL,
+				      DEFAULT_RATELIMIT_BURST);
+
+	if (__ratelimit(&rs))
+		return 0;
 
 	reason = dmar_get_fault_reason(fault_reason, &fault_type);
 
 	if (fault_type == INTR_REMAP)
-		pr_err("INTR-REMAP: Request device [[%02x:%02x.%d] "
-		       "fault index %llx\n"
-			"INTR-REMAP:[fault reason %02d] %s\n",
-			(source_id >> 8), PCI_SLOT(source_id & 0xFF),
-			PCI_FUNC(source_id & 0xFF), addr >> 48,
-			fault_reason, reason);
+		pr_err("[INTR-REMAP] Request device [%02x:%02x.%d] fault index %llx [fault reason %02d] %s\n",
+		       source_id >> 8, PCI_SLOT(source_id & 0xFF),
+		       PCI_FUNC(source_id & 0xFF), addr >> 48,
+		       fault_reason, reason);
 	else
-		pr_err("DMAR:[%s] Request device [%02x:%02x.%d] "
-		       "fault addr %llx \n"
-		       "DMAR:[fault reason %02d] %s\n",
-		       (type ? "DMA Read" : "DMA Write"),
-		       (source_id >> 8), PCI_SLOT(source_id & 0xFF),
-		       PCI_FUNC(source_id & 0xFF), addr, fault_reason, reason);
+		pr_err("[%s] Request device [%02x:%02x.%d] fault addr %llx [fault reason %02d] %s\n",
+		       type ? "DMA Read" : "DMA Write",
+		       source_id >> 8, PCI_SLOT(source_id & 0xFF),
+		       PCI_FUNC(source_id & 0xFF), addr,
+		       fault_reason, reason);
+
 	return 0;
 }