Re: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed and whether it's limited
From: Tal Gilboa
Date: Mon Apr 02 2018 - 17:09:22 EST
On 4/2/2018 11:25 PM, Keller, Jacob E wrote:
-----Original Message-----
From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
Sent: Monday, April 02, 2018 12:58 PM
To: Keller, Jacob E <jacob.e.keller@xxxxxxxxx>
Cc: Tal Gilboa <talgi@xxxxxxxxxxxx>; Tariq Toukan <tariqt@xxxxxxxxxxxx>; Ariel
Elior <ariel.elior@xxxxxxxxxx>; Ganesh Goudar <ganeshgr@xxxxxxxxxxx>;
Kirsher, Jeffrey T <jeffrey.t.kirsher@xxxxxxxxx>; everest-linux-l2@xxxxxxxxxx;
intel-wired-lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
kernel@xxxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed
and whether it's limited
On Mon, Apr 02, 2018 at 04:25:17PM +0000, Keller, Jacob E wrote:
-----Original Message-----
From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
Sent: Friday, March 30, 2018 2:05 PM
To: Tal Gilboa <talgi@xxxxxxxxxxxx>
Cc: Tariq Toukan <tariqt@xxxxxxxxxxxx>; Keller, Jacob E
<jacob.e.keller@xxxxxxxxx>; Ariel Elior <ariel.elior@xxxxxxxxxx>; Ganesh
Goudar <ganeshgr@xxxxxxxxxxx>; Kirsher, Jeffrey T
<jeffrey.t.kirsher@xxxxxxxxx>; everest-linux-l2@xxxxxxxxxx; intel-wired-
lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
linux-pci@xxxxxxxxxxxxxxx
Subject: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed
and
whether it's limited
From: Tal Gilboa <talgi@xxxxxxxxxxxx>
Add pcie_print_link_status(). This logs the current settings of the link
(speed, width, and total available bandwidth).
If the device is capable of more bandwidth but is limited by a slower
upstream link, we include information about the link that limits the
device's performance.
The user may be able to move the device to a different slot for better
performance.
This provides a unified method for all PCI devices to report status and
issues, instead of each device reporting in a different way, using
different code.
Signed-off-by: Tal Gilboa <talgi@xxxxxxxxxxxx>
[bhelgaas: changelog, reword log messages, print device capabilities when
not limited]
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
---
drivers/pci/pci.c | 29 +++++++++++++++++++++++++++++
include/linux/pci.h | 1 +
2 files changed, 30 insertions(+)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e00d56b12747..cec7aed09f6b 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5283,6 +5283,35 @@ u32 pcie_bandwidth_capable(struct pci_dev *dev,
enum pci_bus_speed *speed,
return *width * PCIE_SPEED2MBS_ENC(*speed);
}
+/**
+ * pcie_print_link_status - Report the PCI device's link speed and width
+ * @dev: PCI device to query
+ *
+ * Report the available bandwidth at the device. If this is less than the
+ * device is capable of, report the device's maximum possible bandwidth and
+ * the upstream link that limits its performance to less than that.
+ */
+void pcie_print_link_status(struct pci_dev *dev)
+{
+ enum pcie_link_width width, width_cap;
+ enum pci_bus_speed speed, speed_cap;
+ struct pci_dev *limiting_dev = NULL;
+ u32 bw_avail, bw_cap;
+
+ bw_cap = pcie_bandwidth_capable(dev, &speed_cap, &width_cap);
+ bw_avail = pcie_bandwidth_available(dev, &limiting_dev, &speed,
&width);
+
+ if (bw_avail >= bw_cap)
+ pci_info(dev, "%d Mb/s available bandwidth (%s x%d link)\n",
+ bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
+ else
+ pci_info(dev, "%d Mb/s available bandwidth, limited by %s x%d
link at %s (capable of %d Mb/s with %s x%d link)\n",
+ bw_avail, PCIE_SPEED2STR(speed), width,
+ limiting_dev ? pci_name(limiting_dev) : "<unknown>",
+ bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
+}
Personally, I would make thic last one a pci_warn() to indicate it at a
higher log level, but I'm ok with the wording, and if consensus is that
this should be at info, I'm ok with that.
Tal's original patch did have a pci_warn() here, and we went back and
forth a bit. They get bug reports when a device doesn't perform as
expected, which argues for pci_warn(). But they also got feedback
saying warnings are a bit too much, which argues for pci_info() [1]
I don't have a really strong opinion either way. I have a slight
preference for info because the user may not be able to do anything
about it (there may not be a faster slot available), and I think
distros are usually configured so a warning interrupts the smooth
graphical boot.
It looks like mlx4, fm10k, and ixgbe currently use warnings, while
bnx2x, bnxt_en, and cxgb4 use info. It's a tie so far :)
[1] https://lkml.kernel.org/r/e47f3628-b56c-4d0a-f18b-
5ffaf261ccc0@xxxxxxxxxxxx
With that information, I'm fine with the proposal to display this as only an info. The message is still printed and can be used for debugging purposes, and I think that's really enough.
Here's a proposal for printing the bandwidth as "x.xxx Gb/s":
Nice, I like that also.
Regards,
Jake
Same here for both.