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SubjectRe: [PATCH v4 7/7] x86/tlb: add tlb_flushall_factor into sysfs for user testing/tuning
On Thu, May 10, 2012 at 01:00:13PM +0800, Alex Shi wrote:
> kernel will replace cr3 rewrite with invlpg when
> tlb_flush_entries <= active_tlb_entries / 2^tlb_flushall_factor
> if tlb_flushall_factor is -1, kernel won't do this replacement.
>
> User can modify its value according to specific applications.
>
> Signed-off-by: Alex Shi <alex.shi@intel.com>
> ---
> Documentation/ABI/testing/sysfs-devices-system-cpu | 12 ++++++
> arch/x86/Kconfig.debug | 11 ++++++
> arch/x86/kernel/cpu/common.c | 37 ++++++++++++++++++++
> drivers/base/cpu.c | 4 ++
> include/linux/cpu.h | 4 ++
> 5 files changed, 68 insertions(+), 0 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index e7be75b..05f8eb7 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -78,6 +78,18 @@ Description: Dynamic addition and removal of CPU's. This is not hotplug
> the system. Information writtento the file to remove CPU's
> is architecture specific.
>
> +What: /sys/devices/system/cpu/tlb_flushall_factor
> +Date: May 2012
> +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
> +Description: tlb_flushall_factor show and setting interface
> + tlb_flushall_factor shows the balance point in replacing cr3
> + writting with multiple 'invlpg'. It will do this replacement
> + when flush_tlb_lines <= active_lines/2^tlb_flushall_factor
> + If tlb_flushall_factor is -1, means the replacement will be
> + disabled.
> +
> + User can set this for the specific CPU or application.

Nowhere do you say this is x86 only, please fix that.

> +
> What: /sys/devices/system/cpu/cpu#/node
> Date: October 2009
> Contact: Linux memory management mailing list <linux-mm@kvack.org>
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index e46c214..5b87493 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -129,6 +129,17 @@ config DOUBLEFAULT
> option saves about 4k and might cause you much additional grey
> hair.
>
> +config DEBUG_TLBFLUSH
> + bool "Enable user level tlb flush all setting"
> + depends on DEBUG_KERNEL && (X86_64 || X86_INVLPG)
> + ---help---
> + This option allows user tune tlb_flushall_factor knob that under
> + /sys/devices/system/cpu, set to -1 means do tlb flush all for any
> + multiple tlb lines evacuation demand. Otherwise kernel will use
> + multiple 'invlpg' for the demand when
> + flush_lines <= active_tlb_lines / 2^tlb_flushall_factor
> + If in doubt, say "N"

Yeah, another tunable that no one knows how to use.

Really, why is this here at all? As others pointed out, this really
looks like a debugging thing that almost no one will ever need, so
please, put it in debugfs.

> +
> config IOMMU_DEBUG
> bool "Enable IOMMU debugging"
> depends on GART_IOMMU && DEBUG_KERNEL
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 8879d20..d1986c6 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -481,6 +481,43 @@ void __cpuinit cpu_detect_tlb(struct cpuinfo_x86 *c)
> tlb_flushall_factor);
> }
>
> +#ifdef CONFIG_DEBUG_TLBFLUSH
> +static ssize_t __tlb_flushall_factor_store(const char *buf,
> + size_t count, int smt)
> +{
> + short factor = 0;
> +
> + if (sscanf(buf, "%hd", &factor) != 1)
> + return -EINVAL;
> +
> + tlb_flushall_factor = factor;
> +
> + return count;
> +}
> +
> +static ssize_t tlb_flushall_factor_show(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%hd\n", tlb_flushall_factor);
> +}
> +static ssize_t tlb_flushall_factor_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + return __tlb_flushall_factor_store(buf, count, 0);
> +}
> +
> +static DEVICE_ATTR(tlb_flushall_factor, 0644,
> + tlb_flushall_factor_show,
> + tlb_flushall_factor_store);
> +
> +int __init create_sysfs_tlb_flushall_factor(struct device *dev)
> +{
> + return device_create_file(dev, &dev_attr_tlb_flushall_factor);
> +}
> +#endif
> +
> void __cpuinit detect_ht(struct cpuinfo_x86 *c)
> {
> #ifdef CONFIG_X86_HT
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index adf937b..dc0f77b 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -331,6 +331,10 @@ void __init cpu_dev_init(void)
>
> cpu_dev_register_generic();
>
> +#ifdef CONFIG_DEBUG_TLBFLUSH
> + create_sysfs_tlb_flushall_factor(cpu_subsys.dev_root);
> +#endif

Do the #ifdef in the .h file, not the .c file please, no matter how you
end up doing this (debugfs vs. sysfs.)

thanks,

greg k-h


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