[PATCH 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 style.

Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
---
 kdumpctl | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kdumpctl b/kdumpctl
index cb6f004..507f2dc 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -106,9 +106,11 @@ append_cmdline()
 }
 
 # 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
-- 
1.8.3.1

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

[Xunlei Pang]

Adjust 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 ensure the minium number of
cpus to be used by kdump.

Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
---
 kdumpctl | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git a/kdumpctl b/kdumpctl
index 507f2dc..b633c34 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -105,6 +105,81 @@ append_cmdline()
 	echo $cmdline
 }
 
+# Adjust 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 we adjust the
+# "nr_cpus=X" here to make kdump work properly.
+try_to_adjust_kdump_cpus()
+{
+	local nr_old nr_min nr_max nr
+	local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
+
+	# Special treatment for x86_64 only currently.
+	if [ $arch != "x86_64" ]; then
+		return
+	fi
+
+	# We only care about "nr_cpus=X" format for x86.
+	nr_old=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | wc -l)
+	if [ $nr_old -eq 0 ] ; then
+		# Do not need to process if no valid "nr_cpus=X" specified.
+		return
+	fi
+
+	# Get value X of "nr_cpus=X"
+	nr_old=$(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 mininum value.
+	for nr in $nr_old; do
+		if [ $nr -gt 0 ]; then
+			nr_old=$nr
+			break
+		fi
+	done
+	if [ -z "$nr_old" ]; then
+		echo "Warning: Wrong \"nr_cpus=\" kernel cmdline detected"
+		return
+	fi
+
+	# Online cpus in first kernel.
+	nr_max=$(nproc)
+
+	# Estimated minium cpus required by irqs(vectors), we roughly
+	# use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as the max
+	# supported vectors can be allocated to io devices per cpu.
+	nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
+	# As nr_min is a ballpart figure, also some high-numbered vectors
+	# are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
+	# variance for safety.
+	#
+	# We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
+	# 132 irqs under /proc/irq/, it boots successfully with "nr_cpus=1".
+	# (224-132)=92, choose 64 as the variance seems ok?
+	nr_min=$(($nr_min + 64))
+
+	nr_min=$(($nr_min + 224 - 1))
+	nr_min=$(($nr_min / 224))
+	if [ $nr_min -gt 1 ]; then
+		# The system seems to have tons of irqs, add one more cpu
+		# for further safety.
+		nr_min=$(($nr_min + 1))
+		# Round up to an even number.
+		nr_min=$(($nr_min + $nr_min % 2))
+	fi
+
+	if [ $nr_min -gt $nr_max ]; then
+		nr_min=$nr_max
+	fi
+
+	if [ $nr_old -ge $nr_min ]; then
+		return
+	fi
+
+	cmdline=$(remove_cmdline_param "$cmdline" nr_cpus)
+	cmdline="${cmdline} nr_cpus=${nr_min}"
+	KDUMP_COMMANDLINE=$cmdline
+	echo "CPU vector under pressure with \"nr_cpus=$nr_old\", replaced it
with \"nr_cpus=$nr_min\""
+}
+
 # This function performs a series of edits on the command line
 # Store the final result in global $KDUMP_COMMANDLINE.
 prepare_cmdline()
@@ -134,6 +209,8 @@ prepare_cmdline()
 	fi
 
 	KDUMP_COMMANDLINE=$cmdline
+
+	try_to_adjust_kdump_cpus
 }
 
 
-- 
1.8.3.1

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

[Xunlei Pang]

On 12/23/2016 at 04:02 PM, Xunlei Pang wrote:
>  Adjust 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 ensure the minium number of
>  cpus to be used by kdump.
>
>  Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
>  ---
>   kdumpctl | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 77 insertions(+)
>
>  diff --git a/kdumpctl b/kdumpctl
>  index 507f2dc..b633c34 100755
>  --- a/kdumpctl
>  +++ b/kdumpctl
>  @@ -105,6 +105,81 @@ append_cmdline()
>   	echo $cmdline
>   }
>   
>  +# Adjust the number of cpus for kdump kernel to boot with.
>  +# We met an issue for x86_64: kdump runs out of vectors with
>  +# "nr_cpus=1" when requesting tons of irqs, so we adjust the
>  +# "nr_cpus=X" here to make kdump work properly.
>  +try_to_adjust_kdump_cpus()
>  +{
>  +	local nr_old nr_min nr_max nr
>  +	local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
>  +
>  +	# Special treatment for x86_64 only currently.
>  +	if [ $arch != "x86_64" ]; then
>  +		return
>  +	fi
>  +
>  +	# We only care about "nr_cpus=X" format for x86.
>  +	nr_old=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | wc -l)
>  +	if [ $nr_old -eq 0 ] ; then
>  +		# Do not need to process if no valid "nr_cpus=X" specified.
>  +		return
>  +	fi
>  +
>  +	# Get value X of "nr_cpus=X"
>  +	nr_old=$(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 mininum value.
>  +	for nr in $nr_old; do
>  +		if [ $nr -gt 0 ]; then
>  +			nr_old=$nr
>  +			break
>  +		fi
>  +	done
>  +	if [ -z "$nr_old" ]; then
>  +		echo "Warning: Wrong \"nr_cpus=\" kernel cmdline detected"
>  +		return
>  +	fi
>  +
>  +	# Online cpus in first kernel.
>  +	nr_max=$(nproc)
>  +
>  +	# Estimated minium cpus required by irqs(vectors), we roughly
>  +	# use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as the max
>  +	# supported vectors can be allocated to io devices per cpu.
>  +	nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
>  +	# As nr_min is a ballpart figure, also some high-numbered vectors
>  +	# are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
>  +	# variance for safety.
>  +	#
>  +	# We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
>  +	# 132 irqs under /proc/irq/, it boots successfully with "nr_cpus=1".
>  +	# (224-132)=92, choose 64 as the variance seems ok?
>  +	nr_min=$(($nr_min + 64))
>  +
>  +	nr_min=$(($nr_min + 224 - 1))
>  +	nr_min=$(($nr_min / 224)) 
Seems I should subtract 64 from 224, that is per cpu data:
256 total vectors per cpu, vector for external irq starts from FIRST_EXTERNAL_VECTOR(32),
end at "first system vector(latest is 0xef)"  with our variance set to 64.
256 - 32 - 64 = 160

nr_min=$(($nr_min + 160 - 1))
nr_min=$(($nr_min / 160))

Regards,
Xunlei

>  +	if [ $nr_min -gt 1 ]; then
>  +		# The system seems to have tons of irqs, add one more cpu
>  +		# for further safety.
>  +		nr_min=$(($nr_min + 1))
>  +		# Round up to an even number.
>  +		nr_min=$(($nr_min + $nr_min % 2))
>  +	fi
>  +
>  +	if [ $nr_min -gt $nr_max ]; then
>  +		nr_min=$nr_max
>  +	fi
>  +
>  +	if [ $nr_old -ge $nr_min ]; then
>  +		return
>  +	fi
>  +
>  +	cmdline=$(remove_cmdline_param "$cmdline" nr_cpus)
>  +	cmdline="${cmdline} nr_cpus=${nr_min}"
>  +	KDUMP_COMMANDLINE=$cmdline
>  +	echo "CPU vector under pressure with \"nr_cpus=$nr_old\", replaced it
> with \"nr_cpus=$nr_min\""
>  +}
>  +
>   # This function performs a series of edits on the command line
>   # Store the final result in global $KDUMP_COMMANDLINE.
>   prepare_cmdline()
>  @@ -134,6 +209,8 @@ prepare_cmdline()
>   	fi
>   
>   	KDUMP_COMMANDLINE=$cmdline
>  +
>  +	try_to_adjust_kdump_cpus
>   }
>   
>

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

[Baoquan He]

Hi Xunlei,

As we discussed in meeting, I personally tend to agree not do it this
way. Mainly because it's a corner case and there isn't a clear judgement
to figure out what system could meet the corner case. So it will spread
out into each system, and may bring later maintenance cost though
unpredicted now. Maybe can fix it later when customer has a specific
request to fix this.

Warn user of the danger, or let customer adjust nr_cpus manually, either
is fine to me. 

Thanks
Baoquan

On 12/23/16 at 04:02pm, Xunlei Pang wrote:
> Adjust 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 ensure the minium number of
> cpus to be used by kdump.
> 
> Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
> ---
>  kdumpctl | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/kdumpctl b/kdumpctl
> index 507f2dc..b633c34 100755
> --- a/kdumpctl
> +++ b/kdumpctl
> @@ -105,6 +105,81 @@ append_cmdline()
>  	echo $cmdline
>  }
>  
> +# Adjust the number of cpus for kdump kernel to boot with.
> +# We met an issue for x86_64: kdump runs out of vectors with
> +# "nr_cpus=1" when requesting tons of irqs, so we adjust the
> +# "nr_cpus=X" here to make kdump work properly.
> +try_to_adjust_kdump_cpus()
> +{
> +	local nr_old nr_min nr_max nr
> +	local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
> +
> +	# Special treatment for x86_64 only currently.
> +	if [ $arch != "x86_64" ]; then
> +		return
> +	fi
> +
> +	# We only care about "nr_cpus=X" format for x86.
> +	nr_old=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | wc -l)
> +	if [ $nr_old -eq 0 ] ; then
> +		# Do not need to process if no valid "nr_cpus=X" specified.
> +		return
> +	fi
> +
> +	# Get value X of "nr_cpus=X"
> +	nr_old=$(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 mininum value.
> +	for nr in $nr_old; do
> +		if [ $nr -gt 0 ]; then
> +			nr_old=$nr
> +			break
> +		fi
> +	done
> +	if [ -z "$nr_old" ]; then
> +		echo "Warning: Wrong \"nr_cpus=\" kernel cmdline detected"
> +		return
> +	fi
> +
> +	# Online cpus in first kernel.
> +	nr_max=$(nproc)
> +
> +	# Estimated minium cpus required by irqs(vectors), we roughly
> +	# use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as the max
> +	# supported vectors can be allocated to io devices per cpu.
> +	nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
> +	# As nr_min is a ballpart figure, also some high-numbered vectors
> +	# are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
> +	# variance for safety.
> +	#
> +	# We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
> +	# 132 irqs under /proc/irq/, it boots successfully with "nr_cpus=1".
> +	# (224-132)=92, choose 64 as the variance seems ok?
> +	nr_min=$(($nr_min + 64))
> +
> +	nr_min=$(($nr_min + 224 - 1))
> +	nr_min=$(($nr_min / 224))
> +	if [ $nr_min -gt 1 ]; then
> +		# The system seems to have tons of irqs, add one more cpu
> +		# for further safety.
> +		nr_min=$(($nr_min + 1))
> +		# Round up to an even number.
> +		nr_min=$(($nr_min + $nr_min % 2))
> +	fi
> +
> +	if [ $nr_min -gt $nr_max ]; then
> +		nr_min=$nr_max
> +	fi
> +
> +	if [ $nr_old -ge $nr_min ]; then
> +		return
> +	fi
> +
> +	cmdline=$(remove_cmdline_param "$cmdline" nr_cpus)
> +	cmdline="${cmdline} nr_cpus=${nr_min}"
> +	KDUMP_COMMANDLINE=$cmdline
> +	echo "CPU vector under pressure with \"nr_cpus=$nr_old\", replaced
it with \"nr_cpus=$nr_min\""
> +}
> +
>  # This function performs a series of edits on the command line
>  # Store the final result in global $KDUMP_COMMANDLINE.
>  prepare_cmdline()
> @@ -134,6 +209,8 @@ prepare_cmdline()
>  	fi
>  
>  	KDUMP_COMMANDLINE=$cmdline
> +
> +	try_to_adjust_kdump_cpus
>  }
>  
>  
> -- 
> 1.8.3.1
> _______________________________________________
> kexec mailing list -- kexec(a)lists.fedoraproject.org
> To unsubscribe send an email to kexec-leave(a)lists.fedoraproject.org

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

[Xunlei Pang]

On 01/03/2017 at 02:41 PM, Baoquan He wrote:
>  Hi Xunlei,
>
>  As we discussed in meeting, I personally tend to agree not do it this
>  way. Mainly because it's a corner case and there isn't a clear judgement
>  to figure out what system could meet the corner case. So it will spread
>  out into each system, and may bring later maintenance cost though
>  unpredicted now. Maybe can fix it later when customer has a specific
>  request to fix this.
>
>  Warn user of the danger, or let customer adjust nr_cpus manually, either
>  is fine to me.  
Hi Baoquan,

Thanks for the comments.
Yes, I'd prefer throwing some warnings when service restarts to tip users.

Regards,
Xunlei

>  Thanks
>  Baoquan
>
>  On 12/23/16 at 04:02pm, Xunlei Pang wrote:
> > Adjust 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 ensure the minium number of
> > cpus to be used by kdump.
> >
> > Signed-off-by: Xunlei Pang <xlpang(a)redhat.com&gt;
> > ---
> >  kdumpctl | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 77 insertions(+)
> >
> > diff --git a/kdumpctl b/kdumpctl
> > index 507f2dc..b633c34 100755
> > --- a/kdumpctl
> > +++ b/kdumpctl
> > @@ -105,6 +105,81 @@ append_cmdline()
> >  	echo $cmdline
> >  }
> >  
> > +# Adjust the number of cpus for kdump kernel to boot with.
> > +# We met an issue for x86_64: kdump runs out of vectors with
> > +# "nr_cpus=1" when requesting tons of irqs, so we adjust the
> > +# "nr_cpus=X" here to make kdump work properly.
> > +try_to_adjust_kdump_cpus()
> > +{
> > +	local nr_old nr_min nr_max nr
> > +	local arch=$(uname -m) cmdline=$KDUMP_COMMANDLINE
> > +
> > +	# Special treatment for x86_64 only currently.
> > +	if [ $arch != "x86_64" ]; then
> > +		return
> > +	fi
> > +
> > +	# We only care about "nr_cpus=X" format for x86.
> > +	nr_old=$(echo $cmdline | grep -o "nr_cpus=[0-9]*" | wc -l)
> > +	if [ $nr_old -eq 0 ] ; then
> > +		# Do not need to process if no valid "nr_cpus=X" specified.
> > +		return
> > +	fi
> > +
> > +	# Get value X of "nr_cpus=X"
> > +	nr_old=$(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 mininum value.
> > +	for nr in $nr_old; do
> > +		if [ $nr -gt 0 ]; then
> > +			nr_old=$nr
> > +			break
> > +		fi
> > +	done
> > +	if [ -z "$nr_old" ]; then
> > +		echo "Warning: Wrong \"nr_cpus=\" kernel cmdline detected"
> > +		return
> > +	fi
> > +
> > +	# Online cpus in first kernel.
> > +	nr_max=$(nproc)
> > +
> > +	# Estimated minium cpus required by irqs(vectors), we roughly
> > +	# use 256-32(see kernel FIRST_EXTERNAL_VECTOR)=224 as the max
> > +	# supported vectors can be allocated to io devices per cpu.
> > +	nr_min=$(ls /proc/irq/ -l | grep ^d | wc -l)
> > +	# As nr_min is a ballpart figure, also some high-numbered vectors
> > +	# are consumed by the kernel(see FIRST_SYSTEM_VECTOR), we need a
> > +	# variance for safety.
> > +	#
> > +	# We got a large machine with 240 cpus, 6TB memory, 8 iommus, and
> > +	# 132 irqs under /proc/irq/, it boots successfully with "nr_cpus=1".
> > +	# (224-132)=92, choose 64 as the variance seems ok?
> > +	nr_min=$(($nr_min + 64))
> > +
> > +	nr_min=$(($nr_min + 224 - 1))
> > +	nr_min=$(($nr_min / 224))
> > +	if [ $nr_min -gt 1 ]; then
> > +		# The system seems to have tons of irqs, add one more cpu
> > +		# for further safety.
> > +		nr_min=$(($nr_min + 1))
> > +		# Round up to an even number.
> > +		nr_min=$(($nr_min + $nr_min % 2))
> > +	fi
> > +
> > +	if [ $nr_min -gt $nr_max ]; then
> > +		nr_min=$nr_max
> > +	fi
> > +
> > +	if [ $nr_old -ge $nr_min ]; then
> > +		return
> > +	fi
> > +
> > +	cmdline=$(remove_cmdline_param "$cmdline" nr_cpus)
> > +	cmdline="${cmdline} nr_cpus=${nr_min}"
> > +	KDUMP_COMMANDLINE=$cmdline
> > +	echo "CPU vector under pressure with \"nr_cpus=$nr_old\", replaced
> it with \"nr_cpus=$nr_min\""
> > +}
> > +
> >  # This function performs a series of edits on the command line
> >  # Store the final result in global $KDUMP_COMMANDLINE.
> >  prepare_cmdline()
> > @@ -134,6 +209,8 @@ prepare_cmdline()
> >  	fi
> >  
> >  	KDUMP_COMMANDLINE=$cmdline
> > +
> > +	try_to_adjust_kdump_cpus
> >  }
> >  
> >  
> > -- 
> > 1.8.3.1
> > _______________________________________________
> > kexec mailing list -- kexec(a)lists.fedoraproject.org
> > To unsubscribe send an email to kexec-leave(a)lists.fedoraproject.org

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

[Dave Young]

On 01/05/17 at 10:51am, Xunlei Pang wrote:
>  On 01/03/2017 at 02:41 PM, Baoquan He wrote:
>  > Hi Xunlei,
>  >
>  > As we discussed in meeting, I personally tend to agree not do it this
>  > way. Mainly because it's a corner case and there isn't a clear judgement
>  > to figure out what system could meet the corner case. So it will spread
>  > out into each system, and may bring later maintenance cost though
>  > unpredicted now. Maybe can fix it later when customer has a specific
>  > request to fix this.
>  >
>  > Warn user of the danger, or let customer adjust nr_cpus manually, either
>  > is fine to me. 
>  
>  Hi Baoquan,
>  
>  Thanks for the comments.
>  Yes, I'd prefer throwing some warnings when service restarts to tip users. 
Xunlei, since we have detected that kdump kernel can not boot with
current values, we still use it with a warning, one may not notice it.
It will 100% fail to boot, so maybe error out is better.

Thanks
Dave

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

[Xunlei Pang]

On 01/05/2017 at 02:02 PM, Dave Young wrote:
>  On 01/05/17 at 10:51am, Xunlei Pang wrote:
> > On 01/03/2017 at 02:41 PM, Baoquan He wrote:
> >> Hi Xunlei,
> >>
> >> As we discussed in meeting, I personally tend to agree not do it this
> >> way. Mainly because it's a corner case and there isn't a clear judgement
> >> to figure out what system could meet the corner case. So it will spread
> >> out into each system, and may bring later maintenance cost though
> >> unpredicted now. Maybe can fix it later when customer has a specific
> >> request to fix this.
> >>
> >> Warn user of the danger, or let customer adjust nr_cpus manually, either
> >> is fine to me. 
> > Hi Baoquan,
> >
> > Thanks for the comments.
> > Yes, I'd prefer throwing some warnings when service restarts to tip users.
>  Xunlei, since we have detected that kdump kernel can not boot with
>  current values, we still use it with a warning, one may not notice it.
>  It will 100% fail to boot, so maybe error out is better. 
It's an estimated figure, it's very likely that it will fail but is not 100%
sure.
In addition, for multiple cpu systems, for interrupts bound to some cpu mask,
one irq actually consumes multiple vectors, it allocates one vector on each cpu
contained in the mask.

If it happens to boot with current value, then error out would be a false-positive
decision.

Regards,
Xunlei

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

[Dave Young]

On 01/05/17 at 03:40pm, Xunlei Pang wrote:
>  On 01/05/2017 at 02:02 PM, Dave Young wrote:
>  > On 01/05/17 at 10:51am, Xunlei Pang wrote:
>  >> On 01/03/2017 at 02:41 PM, Baoquan He wrote:
>  >>> Hi Xunlei,
>  >>>
>  >>> As we discussed in meeting, I personally tend to agree not do it this
>  >>> way. Mainly because it's a corner case and there isn't a clear
> judgement
>  >>> to figure out what system could meet the corner case. So it will spread
>  >>> out into each system, and may bring later maintenance cost though
>  >>> unpredicted now. Maybe can fix it later when customer has a specific
>  >>> request to fix this.
>  >>>
>  >>> Warn user of the danger, or let customer adjust nr_cpus manually, either
>  >>> is fine to me. 
>  >> Hi Baoquan,
>  >>
>  >> Thanks for the comments.
>  >> Yes, I'd prefer throwing some warnings when service restarts to tip users.
>  > Xunlei, since we have detected that kdump kernel can not boot with
>  > current values, we still use it with a warning, one may not notice it.
>  > It will 100% fail to boot, so maybe error out is better.
>  
>  It's an estimated figure, it's very likely that it will fail but is not 100%
> sure.
>  In addition, for multiple cpu systems, for interrupts bound to some cpu mask,
>  one irq actually consumes multiple vectors, it allocates one vector on each cpu
>  contained in the mask.
>  
>  If it happens to boot with current value, then error out would be a false-positive
>  decision. 
Hmm, ok if so it is reasonable to use a warning instead.

Thanks!
Dave