[PATCH] x86: Add a turbo mode sysctl

[PATCH] x86: Add a turbo mode sysctl

[Andy Lutomirski]

Sadly, hardware turbo mode buttons are few and far between in these
degenerate times.  Add a software control at /proc/sys/turbo_mode.

Unfortunately, Linux graphical environments have become very
heavy-weight and are essentially unusable on non-Turbo systems.  The
VT console works very well, though.

Due to KVM limitations, turbo mode is permanently on in a KVM guest.

Signed-off-by: Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 arch/x86/mm/pat.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 61 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index faec01e7a17d..f703d8b1ed20 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -69,6 +69,8 @@ static int __init pat_debug_setup(char *str)
 }
 __setup("debugpat", pat_debug_setup);
 
+static int turbo_mode = 1;
+
 #ifdef CONFIG_X86_PAT
 /*
  * X86 PAT uses page flags arch_1 and uncached together to keep track of
@@ -176,6 +178,62 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
 
 #undef CM
 
+#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
+
+static void update_local_turbo_mode(void *dummy)
+{
+	unsigned long cr0 = read_cr0();
+
+	/*
+	 * KVM doesn't properly handle CD.
+	 *
+	 * XXX: this may interact poorly with CPU hotplug.
+	 */
+
+	if (turbo_mode)
+		write_cr0(cr0 & ~X86_CR0_CD);
+	else
+		write_cr0(cr0 | X86_CR0_CD);
+}
+
+static void update_turbo_mode(void)
+{
+	on_each_cpu(update_local_turbo_mode, NULL, 1);
+
+	if (!turbo_mode)
+		wbinvd();
+}
+
+static int turbo_mode_handler(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp,
+			      loff_t *ppos)
+{
+        int error;
+
+        error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+        if (error)
+                return error;
+
+        if (write)
+		update_turbo_mode();
+
+        return 0;
+}
+
+static int zero, one = 1;
+static struct ctl_table turbo_mode_table[] = {
+	{
+		.procname	= "turbo_mode",
+		.data		= &turbo_mode,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= turbo_mode_handler,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+	{}
+};
+
 /*
  * Update the cache mode to pgprot translation tables according to PAT
  * configuration.
@@ -196,8 +254,6 @@ void pat_init_cache_modes(u64 pat)
 	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
 }
 
-#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
-
 static void pat_bsp_init(u64 pat)
 {
 	u64 tmp_pat;
@@ -1096,6 +1152,9 @@ static int __init pat_memtype_list_init(void)
 		debugfs_create_file("pat_memtype_list", S_IRUSR,
 				    arch_debugfs_dir, NULL, &memtype_fops);
 	}
+
+	register_sysctl_table(turbo_mode_table);
+
 	return 0;
 }
 
-- 
2.5.5

Re: [PATCH] x86: Add a turbo mode sysctl

[Borislav Petkov]

On Fri, Apr 01, 2016 at 08:49:53AM -0700, Andy Lutomirski wrote:
> Sadly, hardware turbo mode buttons are few and far between in these
> degenerate times.  Add a software control at /proc/sys/turbo_mode.
> 
> Unfortunately, Linux graphical environments have become very
> heavy-weight and are essentially unusable on non-Turbo systems.  The
> VT console works very well, though.
> 
> Due to KVM limitations, turbo mode is permanently on in a KVM guest.
> 
> Signed-off-by: Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> ---
>  arch/x86/mm/pat.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 61 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index faec01e7a17d..f703d8b1ed20 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -69,6 +69,8 @@ static int __init pat_debug_setup(char *str)
>  }
>  __setup("debugpat", pat_debug_setup);
>  
> +static int turbo_mode = 1;
> +
>  #ifdef CONFIG_X86_PAT
>  /*
>   * X86 PAT uses page flags arch_1 and uncached together to keep track of
> @@ -176,6 +178,62 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
>  
>  #undef CM
>  
> +#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
> +
> +static void update_local_turbo_mode(void *dummy)
> +{
> +	unsigned long cr0 = read_cr0();
> +
> +	/*
> +	 * KVM doesn't properly handle CD.
> +	 *
> +	 * XXX: this may interact poorly with CPU hotplug.
> +	 */
> +
> +	if (turbo_mode)
> +		write_cr0(cr0 & ~X86_CR0_CD);
> +	else
> +		write_cr0(cr0 | X86_CR0_CD);

Good!

> +}
> +
> +static void update_turbo_mode(void)
> +{
> +	on_each_cpu(update_local_turbo_mode, NULL, 1);
> +
> +	if (!turbo_mode)
> +		wbinvd();
> +}
> +
> +static int turbo_mode_handler(struct ctl_table *table, int write,
> +			      void __user *buffer, size_t *lenp,
> +			      loff_t *ppos)
> +{
> +        int error;
> +
> +        error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> +        if (error)
> +                return error;
> +
> +        if (write)
> +		update_turbo_mode();
> +
> +        return 0;
> +}
> +
> +static int zero, one = 1;
> +static struct ctl_table turbo_mode_table[] = {
> +	{
> +		.procname	= "turbo_mode",

I'd call that "make_shit_faster". Other than that, ACK!

> +		.data		= &turbo_mode,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= turbo_mode_handler,
> +		.extra1		= &zero,
> +		.extra2		= &one,
> +	},
> +	{}
> +};
> +
>  /*
>   * Update the cache mode to pgprot translation tables according to PAT
>   * configuration.
> @@ -196,8 +254,6 @@ void pat_init_cache_modes(u64 pat)
>  	pr_info("x86/PAT: Configuration [0-7]: %s\n", pat_msg);
>  }
>  
> -#define PAT(x, y)	((u64)PAT_ ## y << ((x)*8))
> -
>  static void pat_bsp_init(u64 pat)
>  {
>  	u64 tmp_pat;
> @@ -1096,6 +1152,9 @@ static int __init pat_memtype_list_init(void)
>  		debugfs_create_file("pat_memtype_list", S_IRUSR,
>  				    arch_debugfs_dir, NULL, &memtype_fops);
>  	}
> +
> +	register_sysctl_table(turbo_mode_table);
> +
>  	return 0;
>  }
>  
> -- 
> 2.5.5
> 
> 

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Re: [PATCH] x86: Add a turbo mode sysctl

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1590 bytes --]

Hi Andy,

[auto build test WARNING on tip/x86/core]
[also build test WARNING on v4.6-rc1 next-20160401]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Andy-Lutomirski/x86-Add-a-turbo-mode-sysctl/20160401-235300
config: i386-randconfig-s1-201613 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

>> arch/x86/mm/pat.c:224:25: warning: 'turbo_mode_table' defined but not used [-Wunused-variable]
    static struct ctl_table turbo_mode_table[] = {
                            ^

vim +/turbo_mode_table +224 arch/x86/mm/pat.c

   208				      void __user *buffer, size_t *lenp,
   209				      loff_t *ppos)
   210	{
   211	        int error;
   212	
   213	        error = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
   214	        if (error)
   215	                return error;
   216	
   217	        if (write)
   218			update_turbo_mode();
   219	
   220	        return 0;
   221	}
   222	
   223	static int zero, one = 1;
 > 224	static struct ctl_table turbo_mode_table[] = {
   225		{
   226			.procname	= "turbo_mode",
   227			.data		= &turbo_mode,
   228			.maxlen		= sizeof(int),
   229			.mode		= 0644,
   230			.proc_handler	= turbo_mode_handler,
   231			.extra1		= &zero,
   232			.extra2		= &one,

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 27118 bytes --]

Re: [PATCH] x86: Add a turbo mode sysctl

[Thomas Gleixner]

On Fri, 1 Apr 2016, Andy Lutomirski wrote:
> +static void update_local_turbo_mode(void *dummy)
> +{
> +	unsigned long cr0 = read_cr0();
> +
> +	/*
> +	 * KVM doesn't properly handle CD.
> +	 *
> +	 * XXX: this may interact poorly with CPU hotplug.

Please cc these crazy folks who cleanup the hotplug mess so they can put it on
their todo list.

> +	 */
> +
> +	if (turbo_mode)
> +		write_cr0(cr0 & ~X86_CR0_CD);
> +	else
> +		write_cr0(cr0 | X86_CR0_CD);

I think proper turbo mode disable requires ~(X86_CR0_CD | X86_CR0_NW)

> +static void update_turbo_mode(void)
> +{
> +	on_each_cpu(update_local_turbo_mode, NULL, 1);
> +
> +	if (!turbo_mode)
> +		wbinvd();

You really want to do wbinvd() on each cpu to make sure that each cpu gets out
of that turbo thing.

Thanks,

	tglx

Re: [PATCH] x86: Add a turbo mode sysctl

[Andy Lutomirski]

On Fri, Apr 1, 2016 at 9:10 AM, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org> wrote:
> On Fri, 1 Apr 2016, Andy Lutomirski wrote:
>> +static void update_local_turbo_mode(void *dummy)
>> +{
>> +     unsigned long cr0 = read_cr0();
>> +
>> +     /*
>> +      * KVM doesn't properly handle CD.
>> +      *
>> +      * XXX: this may interact poorly with CPU hotplug.
>
> Please cc these crazy folks who cleanup the hotplug mess so they can put it on
> their todo list.
>
>> +      */
>> +
>> +     if (turbo_mode)
>> +             write_cr0(cr0 & ~X86_CR0_CD);
>> +     else
>> +             write_cr0(cr0 | X86_CR0_CD);
>
> I think proper turbo mode disable requires ~(X86_CR0_CD | X86_CR0_NW)

I thought that made no difference on family 6 and P4 and was actively
dangerous (disabled coherency) before.  At least, that's what the
table of caching modes and the footnote seems to say.

>
>> +static void update_turbo_mode(void)
>> +{
>> +     on_each_cpu(update_local_turbo_mode, NULL, 1);
>> +
>> +     if (!turbo_mode)
>> +             wbinvd();
>
> You really want to do wbinvd() on each cpu to make sure that each cpu gets out
> of that turbo thing.

Nah, this is an explicit optimization to de-turboize as quickly as possible:

"The instruction then issues a special-function bus cycle that directs
external caches to also write
back modified data and another bus cycle to indicate that the external
caches should be invalidated."

I think we should merge this patch and add a special-case so that
calling unlink on turbo_mode sets it to zero.  Then people who rm -rf
/ will brick their systems more slowly :)

--Andy

Re: [PATCH] x86: Add a turbo mode sysctl

[Thomas Gleixner]

On Sat, 2 Apr 2016, Andy Lutomirski wrote:
> On Fri, Apr 1, 2016 at 9:10 AM, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org> wrote:
> >> +     if (turbo_mode)
> >> +             write_cr0(cr0 & ~X86_CR0_CD);
> >> +     else
> >> +             write_cr0(cr0 | X86_CR0_CD);
> >
> > I think proper turbo mode disable requires ~(X86_CR0_CD | X86_CR0_NW)
> 
> I thought that made no difference on family 6 and P4 and was actively
> dangerous (disabled coherency) before.  At least, that's what the
> table of caching modes and the footnote seems to say.

CD=0 and NW=1 result in #GP, which might be your intent as that is definitely
the slowest mode you can achieve. But you should add a comment at least.

> I think we should merge this patch and add a special-case so that
> calling unlink on turbo_mode sets it to zero.  Then people who rm -rf
> / will brick their systems more slowly :)

While at it can you please make a turbo = 0 call when we hit a WARN/BUG/Panic
so the messages spill slower over the screen?

Thanks,

	tglx

Re: [PATCH] x86: Add a turbo mode sysctl

[Borislav Petkov]

On Sun, Apr 03, 2016 at 11:55:34AM +0200, Thomas Gleixner wrote:
> While at it can you please make a turbo = 0 call when we hit a WARN/BUG/Panic
> so the messages spill slower over the screen?

Good idea!

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Re: [PATCH] x86: Add a turbo mode sysctl

[Nikolay Borisov]

On 04/01/2016 06:49 PM, Andy Lutomirski wrote:
> Sadly, hardware turbo mode buttons are few and far between in these
> degenerate times.  Add a software control at /proc/sys/turbo_mode.
> 
> Unfortunately, Linux graphical environments have become very
> heavy-weight and are essentially unusable on non-Turbo systems.  The
> VT console works very well, though.
> 
> Due to KVM limitations, turbo mode is permanently on in a KVM guest.
> 
> Signed-off-by: Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> ---
>  arch/x86/mm/pat.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 61 insertions(+), 2 deletions(-)


The name of the sysctl really sucks, it just control whether caching is
enabled/disabled. Now, having said that I realize there are multiple
sysctl that contain "cache" in their names. But can you come up with a
more descriptive name, directly relating to what the sysctl does and now
what its actual effects are :)? Also, aren't caches enabled by the
kernel when the system is booting, according to SDM1/section 9.3 caches
are disabled after reset and I assume the kernel does enable them when
it's booting?