[PATCH v3 1/2] kdumpctl: change prepare_cmdline() to operate KDUMP_COMMANDLINE directly

[Xunlei Pang]

Since KDUMP_COMMANDLINE is a global variable, prepare_cmdline can
modify it directly instead of echoing back the result. This change
enables it to output messages.

Changed some coding styles.

Acked-by: Dave Young 
Signed-off-by: Xunlei Pang 
---
v1->v2:
Changed some comments.

v2->v3:
No change.
 kdumpctl | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kdumpctl b/kdumpctl
index cb6f004..b2068cc 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -105,10 +105,12 @@ append_cmdline()
    echo $cmdline
 }

-# This function performs a series of edits on the command line
+# This function performs a series of edits on the command line.
+# Store the final result in global $KDUMP_COMMANDLINE.
 prepare_cmdline()
 {
-	local cmdline;
+	local cmdline id
+
    if [ -z "$KDUMP_COMMANDLINE" ]; then
    	cmdline=`cat /proc/cmdline`
    	# 'root' parameter will cause kdump failure in live images
@@ -118,6 +120,7 @@ prepare_cmdline()
    else
    	cmdline=${KDUMP_COMMANDLINE}
    fi
+
    # These params should always be removed
    cmdline=`remove_cmdline_param "$cmdline" crashkernel panic_on_warn`
    # These params can be removed configurably
@@ -125,12 +128,12 @@ prepare_cmdline()

cmdline="${cmdline} ${KDUMP_COMMANDLINE_APPEND}"

-	local id=`get_bootcpu_initial_apicid`
+	id=`get_bootcpu_initial_apicid`
    if [ ! -z ${id} ] ; then
    	cmdline=`append_cmdline "${cmdline}" disable_cpu_apicid ${id}`
    fi

-	echo $cmdline
+	KDUMP_COMMANDLINE=$cmdline
 }

@@ -642,7 +645,7 @@ load_kdump()
    	fi
    fi

-	KDUMP_COMMANDLINE=`prepare_cmdline`
+	prepare_cmdline

# For secureboot enabled machines, use new kexec file based syscall.
    # Old syscall will always fail as it does not have capability to

[PATCH v3 2/2] kdumpctl: sanity check of nr_cpus for x86_64 in case running out of vectors

[Xunlei Pang]

Check the number of cpus for x86_64 kdump kernel to boot with.
We met an issue for x86_64: kdump runs out of vectors with the
default "nr_cpus=1", when requesting tons of irqs.

This patch detects such situation and warns users about the risk.

Signed-off-by: Xunlei Pang 
---
v1->v2:
- When detecting risky cpu vectors, we just warn users instead of
  modifying "nr_cpus=X" forcely.
- Improved code comments.
- Replaced nr_old with nr_origin, and improved some logic.

v2->v3:
- Improved the code according to Dave's suggestions.

kdumpctl | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/kdumpctl b/kdumpctl
index b2068cc..9dfc9e2 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -105,6 +105,77 @@ append_cmdline()
    echo $cmdline
 }

+# Check the number of cpus for kdump kernel to boot with.
+# We met an issue for x86_64: kdump runs out of vectors with
+# "nr_cpus=1" when requesting tons of irqs, so here we check
+# "nr_cpus=X" and warn users if kdump probably can't work.
+check_kdump_cpus()
+{
+	local nr nr_search nr_origin nr_min nr_max
+	local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
+
+	# Special treatment for x86_64 only currently.
+	if [ $arch != "x86_64" ]; then
+		return
+	fi
+
+	# We only care about "nr_cpus=X" format for x86.
+	nr_search=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | cut -d "=" -f2 | grep "[0-9]" | sort)
+	# In case there are multiple "nr_cpus=X", get the lowest non-zero value.
+	for nr in $nr_search; do
+		if [ $nr -gt 0 ]; then
+			nr_origin=$nr
+			break
+		fi
+	done
+	if [ -z "$nr_origin" ]; then
+		return
+	fi
+
+	# Online cpus in first kernel.
+	nr_max=$(grep -c '^processor' /proc/cpuinfo)
+
+	# Calculate estimated minium cpus required by irqs(vectors).
+	nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
+
+	# We roughly use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as
+	# maximum supported vectors can be allocated to io devices percpu.
+	# As nr_min is a ballpart figure, also some high-numbered vectors
+	# are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
+	# variance for safety.
+	#
+	# We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
+	# 12 io-apics, 132 irqs under /proc/irq/, it can boot successfully
+	# with "nr_cpus=1". (256-32-132)=92, so choosing 64 as the variance
+	# seems ok. Then we get the max external irqs supported per cpu:
+	# (256-32-64)=160 as the dividend.
+	nr_min=$(($nr_min + 160 - 1))
+	nr_min=$(($nr_min / 160))
+	if [ $nr_min -gt 1 ]; then
+		# The system seems to have tons of interrupts. while interrupts
+		# with multiple-cpu affinity can consume multiple vectors, with
+		# one vector for each cpu within the affinity mask. Fortunately
+		# for x2apic which is widely used on large modern machines, in
+		# default case of boot, device bringup etc will use a single cpu
+		# for the interrupt affinity to minimize vector pressure.
+		#
+		# For further safety, we add one more cpu and round it up to an
+		# even number which is commonly-used.
+		nr_min=$(($nr_min + 1))
+		nr_min=$(($nr_min + $nr_min % 2))
+	fi
+
+	if [ $nr_min -gt $nr_max ]; then
+		nr_min=$nr_max
+	fi
+
+	if [ $nr_origin -ge $nr_min ]; then
+		return
+	fi
+
+	echo "Warning: nr_cpus=$nr_origin may not be enough for kdump boot, try nr_cpus=$nr_min or larger instead"
+}
+
 # This function performs a series of edits on the command line.
 # Store the final result in global $KDUMP_COMMANDLINE.
 prepare_cmdline()
@@ -134,6 +205,8 @@ prepare_cmdline()
    fi

KDUMP_COMMANDLINE=$cmdline
+
+	check_kdump_cpus
 }

[PATCH v3 2/2] kdumpctl: sanity check of nr_cpus for x86_64 in case running out of vectors

[Dave Young]

Hi, Xunlei

On 01/06/17 at 05:49pm, Xunlei Pang wrote:
> Check the number of cpus for x86_64 kdump kernel to boot with.
> We met an issue for x86_64: kdump runs out of vectors with the
> default "nr_cpus=1", when requesting tons of irqs.
>
> This patch detects such situation and warns users about the risk.
> Signed-off-by: Xunlei Pang
>
> v1->v2:
> When detecting risky cpu vectors, we just warn users instead of
> modifying "nr_cpus=X" forcely.
> Improved code comments.
> Replaced nr_old with nr_origin, and improved some logic.
>
> v2->v3:
> Improved the code according to Dave's suggestions.
>
> kdumpctl | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
>
> diff --git a/kdumpctl b/kdumpctl
> index b2068cc..9dfc9e2 100755
> --- a/kdumpctl
> +++ b/kdumpctl
> @@ -105,6 +105,77 @@ append_cmdline()
>    echo $cmdline
>  }
>
> +# Check the number of cpus for kdump kernel to boot with.
> +# We met an issue for x86_64: kdump runs out of vectors with
> +# "nr_cpus=1" when requesting tons of irqs, so here we check
> +# "nr_cpus=X" and warn users if kdump probably can't work.
> +check_kdump_cpus()
> +{
> local nr nr_search nr_origin nr_min nr_max
> local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
> # Special treatment for x86_64 only currently.
> if [ $arch != "x86_64" ]; then
> return
> fi
> # We only care about "nr_cpus=X" format for x86.
> nr_search=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | cut -d "=" -f2 | grep "[0-9]" | sort)
> # In case there are multiple "nr_cpus=X", get the lowest non-zero value.
> for nr in $nr_search; do
> if [ $nr -gt 0 ]; then
> 	nr_origin=$nr
> 	break
> fi
> done
> if [ -z "$nr_origin" ]; then
> return
> fi

How about just echo $cmdline | grep -e "nr_cpus=1[[:space:]]" 
If it return true then we can regard use 1 to compare with nr_min.
> # Online cpus in first kernel.
> nr_max=$(grep -c '^processor' /proc/cpuinfo)
> # Calculate estimated minium cpus required by irqs(vectors).
> nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
> # We roughly use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as
> # maximum supported vectors can be allocated to io devices percpu.
> # As nr_min is a ballpart figure, also some high-numbered vectors
> # are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
> # variance for safety.
> #
> # We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
> # 12 io-apics, 132 irqs under /proc/irq/, it can boot successfully
> # with "nr_cpus=1". (256-32-132)=92, so choosing 64 as the variance
> # seems ok. Then we get the max external irqs supported per cpu:
> # (256-32-64)=160 as the dividend.
> nr_min=$(($nr_min + 160 - 1))
> nr_min=$(($nr_min / 160))
> if [ $nr_min -gt 1 ]; then
> # The system seems to have tons of interrupts. while interrupts
> # with multiple-cpu affinity can consume multiple vectors, with
> # one vector for each cpu within the affinity mask. Fortunately
> # for x2apic which is widely used on large modern machines, in
> # default case of boot, device bringup etc will use a single cpu
> # for the interrupt affinity to minimize vector pressure.
> #
> # For further safety, we add one more cpu and round it up to an
> # even number which is commonly-used.
> nr_min=$(($nr_min + 1))
> nr_min=$(($nr_min + $nr_min % 2))
> fi
> if [ $nr_min -gt $nr_max ]; then
> nr_min=$nr_max
> fi
> if [ $nr_origin -ge $nr_min ]; then
> return
> fi
> echo "Warning: nr_cpus=$nr_origin may not be enough for kdump boot, try nr_cpus=$nr_min or larger instead"
>
> +}
>
> # This function performs a series of edits on the command line.
>  # Store the final result in global $KDUMP_COMMANDLINE.
>  prepare_cmdline()
> @@ -134,6 +205,8 @@ prepare_cmdline()
>    fi
>
> KDUMP_COMMANDLINE=$cmdline
> check_kdump_cpus
>
> }
>
> -- 
> 1.8.3.1
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