Re: [PATCH v4 2/6] x86,sched: Add support for frequency invariance on SKYLAKE_X

[Peter Zijlstra]

On Wed, Nov 13, 2019 at 01:46:50PM +0100, Giovanni Gherdovich wrote:
> The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
> accounting. On SKYLAKE_X CPUs set freq_max to the highest frequency that can
> be sustained by a group of at least 4 cores.
> 
> From the changelog of commit 31e07522be56 ("tools/power turbostat: fix
> decoding for GLM, DNV, SKX turbo-ratio limits"):
> 
> >   Newer processors do not hard-code the the number of cpus in each bin
> >   to {1, 2, 3, 4, 5, 6, 7, 8}  Rather, they can specify any number
> >   of CPUS in each of the 8 bins:
> >
> >   eg.
> >
> >   ...
> >   37 * 100.0 = 3600.0 MHz max turbo 4 active cores
> >   38 * 100.0 = 3700.0 MHz max turbo 3 active cores
> >   39 * 100.0 = 3800.0 MHz max turbo 2 active cores
> >   39 * 100.0 = 3900.0 MHz max turbo 1 active cores
> >
> >   could now look something like this:
> >
> >   ...
> >   37 * 100.0 = 3600.0 MHz max turbo 16 active cores
> >   38 * 100.0 = 3700.0 MHz max turbo 8 active cores
> >   39 * 100.0 = 3800.0 MHz max turbo 4 active cores
> >   39 * 100.0 = 3900.0 MHz max turbo 2 active cores
> 
> This encoding of turbo levels applies to both SKYLAKE_X and GOLDMONT/GOLDMONT_D,
> but we treat these two classes in separate commits because their freq_max
> values need to be different. For SKX we prefer a lower freq_max in the ratio
> freq_curr/freq_max, allowing load and utilization to overshoot and the
> schedutil governor to be more performance-oriented. Models from the Atom
> series (such as GOLDMONT*) are handled in a forthcoming commit as they have to
> favor power-efficiency over performance.

Can we at least use a single function to decode both? A little like the
below. I'm not married to the naming, but I think it is a little silly
to have 2 different functions to decode the exact same MSRs.

(one could even go as far as to make a boot param to override the {1,4}
default core count for these things)

---

Index: linux-2.6/arch/x86/kernel/smpboot.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6/arch/x86/kernel/smpboot.c
@@ -1863,27 +1863,6 @@ static const struct x86_cpu_id has_glm_t
 	{}
 };

-static bool glm_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
-{
-	int err;
-
-	if (!x86_match_cpu(has_glm_turbo_ratio_limits))
-		return false;
-
-	err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
-	if (err)
-		return false;
-
-	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, turbo_ratio);
-	if (err)
-		return false;
-
-	*ratio = (*ratio >> 8) & 0xFF;        /* max P state ratio */
-	*turbo_ratio = *turbo_ratio & 0xFF;   /* highest turbo ratio */
-
-	return true;
-}
-
 static int get_knl_turbo_ratio(u64 *turbo_ratio)
 {
 	u64 msr;
@@ -1933,53 +1912,35 @@ static bool knl_set_cpu_max_freq(u64 *ra
 	return true;
 }

-static int get_turbo_ratio_group(u64 *turbo_ratio)
+static bool skx_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio, int size)
 {
-	u64 ratio, core_counts;
-	u32 group_size = 0;
-	int err, i, found = 0;
+	u64 ratios, counts;
+	u32 group_size;
+	int err, i;

-	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &ratio);
-	if (err)
-		return err;
-
-	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT1, &core_counts);
+	err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
 	if (err)
-		return err;
-
-	for (i = 0; i < 64; i += 8) {
-		group_size = (core_counts >> i) & 0xFF;
-		if (group_size >= 4) {
-			*turbo_ratio = (ratio >> i) & 0xFF;
-			found = 1;
-			break;
-		}
-	}
-
-	if (!found)
-		return 1;
-
-	return 0;
-}
-
-static bool skx_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
-{
-	int err;
-
-	if (!x86_match_cpu(has_skx_turbo_ratio_limits))
 		return false;

-	err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
+	*ratio = (*ratio >> 8) & 0xFF;                /* max P state ratio */
+
+	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &ratios);
 	if (err)
 		return false;

-	err = get_turbo_ratio_group(turbo_ratio);  /* 4C (circa) turbo ratio */
+	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT1, &counts);
 	if (err)
 		return false;

-	*ratio = (*ratio >> 8) & 0xFF;                /* max P state ratio */
+	for (i = 0; i < 64; i += 8) {
+		group_size = (counts >> i) & 0xFF;
+		if (group_size >= size) {
+			*turbo_ratio = (ratios >> i) & 0xFF;
+			return true;
+		}
+	}

-	return true;
+	return false;
 }

 static bool core_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
@@ -2010,13 +1971,15 @@ static void intel_set_cpu_max_freq(void)
 	if (slv_set_cpu_max_freq(&ratio, &turbo_ratio))
 		goto set_value;

-	if (glm_set_cpu_max_freq(&ratio, &turbo_ratio))
+	if (x86_match_cpu(has_glm_turbo_ratio_limits) &&
+	    skx_set_cpu_max_freq(&ratio, &turbo_ratio, 1))
 		goto set_value;

 	if (knl_set_cpu_max_freq(&ratio, &turbo_ratio))
 		goto set_value;

-	if (skx_set_cpu_max_freq(&ratio, &turbo_ratio))
+	if (x86_match_cpu(has_skx_turbo_ratio_limits) &&
+	    skx_set_cpu_max_freq(&ratio, &turbo_ratio, 4))
 		goto set_value;

 	core_set_cpu_max_freq(&ratio, &turbo_ratio);