x86: Make mwait_usable() heed to "idle=" kernel parameters properly
PATCH RESEND v2 1/1 x86: Make mwait_usable() heed to "idle=" kernel parameters properly
From: Srivatsa S. Bhat <[email protected]>
The checks that exist in mwait_usable() for "idle=" kernel parameters are insufficient. As a result, mwait_usable() can return 1 even if "idle=nomwait" or "idle=poll" or "idle=halt" parameters are passed.
Of these cases, incorrect handling of idle=nomwait is a universal problem since mwait can get used for usual CPU idling. However the rest of the cases are problematic only during CPU Hotplug (offline) because, in the CPU offline path, the function mwait_play_dead() is called, which might result in mwait being used in the offline CPUs, if mwait_usable() happens to return 1.
Fix these issues by checking for the boot time "idle=" kernel parameter properly in mwait_usable().
The first issue (usual cpu idling) is demonstrated below:
Before applying the patch (dmesg snippet):
[ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 0.140606] using mwait in idle threads. <======= mwait being used [ 4.303986] cpuidle: using governor ladder [ 4.308232] cpuidle: using governor menu
After applying the patch:
[ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 4.264100] cpuidle: using governor ladder [ 4.268342] cpuidle: using governor menu
---
arch/x86/kernel/process.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-)
arch/x86/kernel/process.c +8 -0
@@ -618,9 +618,17 @@ int mwait_usable(const struct cpuinfo_x86 *c) {u32 eax, ebx, ecx, edx; +/* Use mwait if idle=mwait boot option is given */ if (boot_option_idle_override ==IDLE_FORCE_MWAIT )return 1 ; +/* +* Any idle= boot option other than idle=mwait means that we must not +* use mwait. Eg: idle=halt or idle=poll or idle=nomwait +*/ +if (boot_option_idle_override !=IDLE_NO_OVERRIDE ) +return 0 ; +if (c->cpuid_level <MWAIT_INFO )return 0 ;
[tip:sched/core] x86/sched: Make mwait_usable() heed to "idle=" kernel parameters properly
Commit-ID: 19209bbb8612004bc20a1f70ff12926f99fe2643 Gitweb: http://git.kernel.org/tip/19209bbb8612004bc20a1f70ff12926f99fe2643 Author: Srivatsa S. Bhat <[email protected]> AuthorDate: Mon, 30 Apr 2012 12:26:56 +0530 Committer: Ingo Molnar <[email protected]> CommitDate: Mon, 7 May 2012 16:27:20 +0200
x86/sched: Make mwait_usable() heed to "idle=" kernel parameters properly
The checks that exist in mwait_usable() for "idle=" kernel parameters are insufficient. As a result, mwait_usable() can return 1 even if "idle=nomwait" or "idle=poll" or "idle=halt" parameters are passed.
Of these cases, incorrect handling of idle=nomwait is a universal problem since mwait can get used for usual CPU idling. However the rest of the cases are problematic only during CPU Hotplug (offline) because, in the CPU offline path, the function mwait_play_dead() is called, which might result in mwait being used in the offline CPUs, if mwait_usable() happens to return 1.
Fix these issues by checking for the boot time "idle=" kernel parameter properly in mwait_usable().
The first issue (usual cpu idling) is demonstrated below:
Before applying the patch (dmesg snippet):
[ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 0.140606] using mwait in idle threads. <======= mwait being used [ 4.303986] cpuidle: using governor ladder [ 4.308232] cpuidle: using governor menu
After applying the patch:
[ 0.000000] Command line: [...] idle=nomwait [ 0.000000] Kernel command line: [...] idle=nomwait [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled. [ 4.264100] cpuidle: using governor ladder [ 4.268342] cpuidle: using governor menu
--- arch/x86/kernel/process.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-)
arch/x86/kernel/process.c +8 -0
@@ -594,9 +594,17 @@ int mwait_usable(const struct cpuinfo_x86 *c) {u32 eax, ebx, ecx, edx; +/* Use mwait if idle=mwait boot option is given */ if (boot_option_idle_override ==IDLE_FORCE_MWAIT )return 1 ; +/* +* Any idle= boot option other than idle=mwait means that we must not +* use mwait. Eg: idle=halt or idle=poll or idle=nomwait +*/ +if (boot_option_idle_override !=IDLE_NO_OVERRIDE ) +return 0 ; +if (c->cpuid_level <MWAIT_INFO )return 0 ;