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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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