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Date: Tue, 13 Sep 2016 15:54:20 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Noam Camus <noamca@...lanox.com>
Cc: <decot@...glers.com>, <ben@...adent.org.uk>, <davem@...emloft.net>,
<linux-kernel@...r.kernel.org>, <xinhui@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5] lib/bitmap.c: enhance bitmap syntax
On Sun, 11 Sep 2016 10:40:29 +0300 Noam Camus <noamca@...lanox.com> wrote:
> From: Noam Camus <noamca@...lanox.com>
>
> Today there are platforms with many CPUs (up to 4K).
> Trying to boot only part of the CPUs may result in too long string.
>
> For example lets take NPS platform that is part of arch/arc.
> This platform have SMP system with 256 cores each with
> 16 HW threads (SMT machine) where HW thread appears as CPU to the kernel.
> In this example there is total of 4K CPUs.
> When one tries to boot only part of the HW threads from each core the
> string representing the map may be long...
> For example if for sake of performance we decided to boot only first half
> of HW threads of each core the map will look like:
> 0-7,16-23,32-39,...,4080-4087
>
> This patch introduce new syntax to accommodate with such use case.
> I added an optional postfix to a range of CPUs which will choose
> according to given modulo the desired range of reminders i.e.:
> <cpus range>:sed_size/group_size
>
> For example, above map can be described in new syntax like this:
> 0-4095:8/16
>
> Note that this patch is backward compatible with current syntax.
>
> Signed-off-by: Noam Camus <noamca@...lanox.com>
> ---
> Documentation/kernel-parameters.txt | 15 ++++++++++
> lib/bitmap.c | 50 ++++++++++++++++++++++++++++++++---
> 2 files changed, 61 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 623502e..4f1e95b 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -33,6 +33,21 @@ can also be entered as
> Double-quotes can be used to protect spaces in values, e.g.:
> param="spaces in here"
>
> +Some of the kernel parameters takes list of CPUs as value e.g.:
> +isolcpus, task_isolation, nohz_full, irqaffinity, rcu_nocbs.
I don't think we have a "task_isolation". What are you trying to
refer to here?
> +The format of this list is:
> +<cpu number>,...,<cpu number>
> +or
> +<cpu number>-<cpu number>
> +(must be a positive range in ascending order)
> +or a mixture
> +<cpu number>,...,<cpu number>-<cpu number>
> +Note that for special case of range one can split range into equal size of groups
> +and for each group to use some amount form the begin of that group.
> +<cpu number>-cpu number>:<used size>/<group size>
> +For example one can add to its command line following parameter:
> +isolcpus=1,2,10-20,100-2000:2/25
> +
I think we can do better here. Please review:
--- a/Documentation/kernel-parameters.txt~lib-bitmapc-enhance-bitmap-syntax-fix
+++ a/Documentation/kernel-parameters.txt
@@ -33,20 +33,36 @@ can also be entered as
Double-quotes can be used to protect spaces in values, e.g.:
param="spaces in here"
-Some of the kernel parameters takes list of CPUs as value e.g.:
-isolcpus, task_isolation, nohz_full, irqaffinity, rcu_nocbs.
-The format of this list is:
-<cpu number>,...,<cpu number>
+cpu lists:
+----------
+
+Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
+nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
+
+ <cpu number>,...,<cpu number>
+
or
-<cpu number>-<cpu number>
-(must be a positive range in ascending order)
+
+ <cpu number>-<cpu number>
+ (must be a positive range in ascending order)
+
or a mixture
+
<cpu number>,...,<cpu number>-<cpu number>
-Note that for special case of range one can split range into equal size of groups
-and for each group to use some amount form the begin of that group.
-<cpu number>-cpu number>:<used size>/<group size>
-For example one can add to its command line following parameter:
-isolcpus=1,2,10-20,100-2000:2/25
+
+Note that for the special case of a range one can split the range into equal
+sized groups and for each group use some amount from the beginning of that
+group:
+
+ <cpu number>-cpu number>:<used size>/<group size>
+
+For example one can add to the command line following parameter:
+
+ isolcpus=1,2,10-20,100-2000:2/25
+
+where the final item represents CPUs 100,101,125,126,150,151,...
+
+
This document may not be entirely up to date and comprehensive. The command
"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
@@ -1776,13 +1792,7 @@ bytes respectively. Such letter suffixes
See Documentation/filesystems/nfs/nfsroot.txt.
irqaffinity= [SMP] Set the default irq affinity mask
- Format:
- <cpu number>,...,<cpu number>
- or
- <cpu number>-<cpu number>
- (must be a positive range in ascending order)
- or a mixture
- <cpu number>,...,<cpu number>-<cpu number>
+ The argument is a cpu list, as described above.
irqfixup [HW]
When an interrupt is not handled search all handlers
@@ -1799,13 +1809,7 @@ bytes respectively. Such letter suffixes
Format: <RDP>,<reset>,<pci_scan>,<verbosity>
isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
- Format:
- <cpu number>,...,<cpu number>
- or
- <cpu number>-<cpu number>
- (must be a positive range in ascending order)
- or a mixture
- <cpu number>,...,<cpu number>-<cpu number>
+ The argument is a cpu list, as described above.
This option can be used to specify one or more CPUs
to isolate from the general SMP balancing and scheduling
@@ -2666,6 +2670,7 @@ bytes respectively. Such letter suffixes
Default: on
nohz_full= [KNL,BOOT]
+ The argument is a cpu list, as described above.
In kernels built with CONFIG_NO_HZ_FULL=y, set
the specified list of CPUs whose tick will be stopped
whenever possible. The boot CPU will be forced outside
@@ -3268,6 +3273,8 @@ bytes respectively. Such letter suffixes
See Documentation/blockdev/ramdisk.txt.
rcu_nocbs= [KNL]
+ The argument is a cpu list, as described above.
+
In kernels built with CONFIG_RCU_NOCB_CPU=y, set
the specified list of CPUs to be no-callback CPUs.
Invocation of these CPUs' RCU callbacks will
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