Re: [Patch -v4 4/4] Make reboot_cpuid a kernel parameter. other cpus.

["H. Peter Anvin" <hpa@zytor.com>]

Why not just support the existing syntax everywhere?

Robin Holt <holt@sgi.com> wrote:

>Moving the reboot=s<##> parameter for x86 to a kernel parameter
>proper.  I did not find any other arch that was specifying the
>reboot cpu.
>
>I left a compatibility mode in there.  The new parameter always
>takes precedence.  I also fixed up the current code to support
>up to cpuid's up to the current max of 4096.
>
>Signed-off-by: Robin Holt <holt@sgi.com>
>To: Ingo Molnar <mingo@redhat.com>
>To: Russ Anderson <rja@sgi.com>
>Cc: Shawn Guo <shawn.guo@linaro.org>
>Cc: Oleg Nesterov <oleg@redhat.com>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: "H. Peter Anvin" <hpa@zytor.com>
>Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
>Cc: Linus Torvalds <torvalds@linux-foundation.org>
>Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
>Cc: Michel Lespinasse <walken@google.com>
>Cc: Oleg Nesterov <oleg@redhat.com>
>Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>Cc: Paul Mackerras <paulus@samba.org>
>Cc: Peter Zijlstra <peterz@infradead.org>
>Cc: Robin Holt <holt@sgi.com>
>Cc: "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>
>Cc: Tejun Heo <tj@kernel.org>
>Cc: the arch/x86 maintainers <x86@kernel.org>
>Cc: Thomas Gleixner <tglx@linutronix.de>
>
>---
>
>Changes since -v3
>- Added a reboot=s#### compatibility mode for x86.
>
> Documentation/kernel-parameters.txt |  2 ++
>arch/x86/kernel/reboot.c            | 39
>+++++++++++++------------------------
> kernel/reboot.c                     |  8 +++++++-
> 3 files changed, 22 insertions(+), 27 deletions(-)
>
>diff --git a/Documentation/kernel-parameters.txt
>b/Documentation/kernel-parameters.txt
>index 4609e81..11ebb48 100644
>--- a/Documentation/kernel-parameters.txt
>+++ b/Documentation/kernel-parameters.txt
>@@ -2597,6 +2597,8 @@ bytes respectively. Such letter suffixes can also
>be entirely omitted.
> 			Format: <reboot_mode>[,<reboot_mode2>[,...]]
> 			See arch/*/kernel/reboot.c or arch/*/kernel/process.c
> 
>+	reboot_cpuid=	[KNL] cpuid to use for reboot/halt, etc operations.
>+
> 	relax_domain_level=
> 			[KNL, SMP] Set scheduler's default relax_domain_level.
> 			See Documentation/cgroups/cpusets.txt.
>diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
>index 76fa1e9..cdcf28f 100644
>--- a/arch/x86/kernel/reboot.c
>+++ b/arch/x86/kernel/reboot.c
>@@ -49,10 +49,6 @@ int reboot_force;
>  */
> static int reboot_default = 1;
> 
>-#ifdef CONFIG_SMP
>-static int reboot_cpu = -1;
>-#endif
>-
> /*
>  * This is set if we need to go through the 'emergency' path.
>  * When machine_emergency_restart() is called, we may be on
>@@ -63,6 +59,8 @@ static int reboot_emergency;
>/* This is set by the PCI code if either type 1 or type 2 PCI is
>detected */
> bool port_cf9_safe = false;
> 
>+extern int reboot_cpuid;
>+
> /*
>* reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old]
>| p[ci]
>  * warm   Don't set the cold reboot flag
>@@ -97,10 +95,14 @@ static int __init reboot_setup(char *str)
> 
> #ifdef CONFIG_SMP
> 		case 's':
>-			if (isdigit(*(str+1))) {
>-				reboot_cpu = (int) (*(str+1) - '0');
>-				if (isdigit(*(str+2)))
>-					reboot_cpu = reboot_cpu*10 + (int)(*(str+2) - '0');
>+			if (reboot_cpuid < 0) {
>+				int coffset;
>+
>+				reboot_cpuid = 0;
>+				for (coffset = 1; isdigit(*(str + coffset)); coffset++) {
>+					reboot_cpuid *= 10;
>+					reboot_cpuid += (int)(*(str+2) - '0');
>+				}
> 			}
> 			/*
> 			 * We will leave sorting out the final value
>@@ -615,25 +617,10 @@ void native_machine_shutdown(void)
> 	/* Stop the cpus and apics */
> #ifdef CONFIG_SMP
> 
>-	/* The boot cpu is always logical cpu 0 */
>-	int reboot_cpu_id = 0;
>-
>-	/* See if there has been given a command line override */
>-	if ((reboot_cpu != -1) && (reboot_cpu < nr_cpu_ids) &&
>-		cpu_online(reboot_cpu))
>-		reboot_cpu_id = reboot_cpu;
>-
>-	/* Make certain the cpu I'm about to reboot on is online */
>-	if (!cpu_online(reboot_cpu_id))
>-		reboot_cpu_id = smp_processor_id();
>-
>-	/* Make certain I only run on the appropriate processor */
>-	set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
>-
> 	/*
>-	 * O.K Now that I'm on the appropriate processor, stop all of the
>-	 * others. Also disable the local irq to not receive the per-cpu
>-	 * timer interrupt which may trigger scheduler's load balance.
>+	 * Stop all of the others. Also disable the local irq to
>+	 * not receive the per-cpu timer interrupt which may trigger
>+	 * scheduler's load balance.
> 	 */
> 	local_irq_disable();
> 	stop_other_cpus();
>diff --git a/kernel/reboot.c b/kernel/reboot.c
>index 8cfef20..b2ef798 100644
>--- a/kernel/reboot.c
>+++ b/kernel/reboot.c
>@@ -10,6 +10,7 @@
> #include <linux/kexec.h>
> #include <linux/kmod.h>
> #include <linux/kmsg_dump.h>
>+#include <linux/moduleparam.h>
> #include <linux/reboot.h>
> #include <linux/suspend.h>
> #include <linux/syscalls.h>
>@@ -69,13 +70,18 @@ int unregister_reboot_notifier(struct
>notifier_block *nb)
> }
> EXPORT_SYMBOL(unregister_reboot_notifier);
> 
>+int reboot_cpuid = -1;
>+core_param(reboot_cpuid, reboot_cpuid, int, 0644);
>+
> void migrate_to_reboot_cpu(void)
> {
> 	/* The boot cpu is always logical cpu 0 */
>-	int reboot_cpu_id = 0;
>+	int reboot_cpu_id = reboot_cpuid;
> 
> 	/* Make certain the cpu I'm about to reboot on is online */
> 	if (!cpu_online(reboot_cpu_id))
>+		reboot_cpu_id = 0;
>+	if (!cpu_online(reboot_cpu_id))
> 		reboot_cpu_id = smp_processor_id();
> 
> 	/* Prevent races with other tasks migrating this task. */

-- 
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