[v4,3/6] x86,sched: Add support for frequency invariance on XEON_PHI_KNL/KNM
diff mbox series

Message ID 20191113124654.18122-4-ggherdovich@suse.cz
State New, archived
Headers show
Series
  • Add support for frequency invariance for (some) x86
Related show

Commit Message

Giovanni Gherdovich Nov. 13, 2019, 12:46 p.m. UTC
The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
accounting. On Xeon Phi CPUs set freq_max to the second-highest frequency
reported by the CPU.

Xeon Phi CPUs such as Knights Landing and Knights Mill typically have either
one or two turbo frequencies; in the former case that's 100 MHz above the base
frequency, in the latter case the two levels are 100 MHz and 200 MHz above
base frequency.

We set freq_max to the second-highest frequency reported by the CPU. This
could be the base frequency (if only one turbo level is available) or the first
turbo level (if two levels are available). The rationale is to compromise
between power efficiency or performance -- going straight to max turbo would
favor efficiency and blindly using base freq would favor performance.

For reference, this is how MSR_TURBO_RATIO_LIMIT must be parsed on a Xeon Phi
to get the available frequencies (taken from a comment in turbostat's sources):

    [0] -- Reserved
    [7:1] -- Base value of number of active cores of bucket 1.
    [15:8] -- Base value of freq ratio of bucket 1.
    [20:16] -- +ve delta of number of active cores of bucket 2.
    i.e. active cores of bucket 2 =
    active cores of bucket 1 + delta
    [23:21] -- Negative delta of freq ratio of bucket 2.
    i.e. freq ratio of bucket 2 =
    freq ratio of bucket 1 - delta
    [28:24]-- +ve delta of number of active cores of bucket 3.
    [31:29]-- -ve delta of freq ratio of bucket 3.
    [36:32]-- +ve delta of number of active cores of bucket 4.
    [39:37]-- -ve delta of freq ratio of bucket 4.
    [44:40]-- +ve delta of number of active cores of bucket 5.
    [47:45]-- -ve delta of freq ratio of bucket 5.
    [52:48]-- +ve delta of number of active cores of bucket 6.
    [55:53]-- -ve delta of freq ratio of bucket 6.
    [60:56]-- +ve delta of number of active cores of bucket 7.
    [63:61]-- -ve delta of freq ratio of bucket 7.

1. PERFORMANCE EVALUATION: TBENCH +5%
2. NEUTRAL BENCHMARKS (ALL OTHERS)
3. TEST SETUP

1. PERFORMANCE EVALUATION: TBENCH +5%
-------------------------------------

A performance evaluation was conducted on a Knights Mill machine (see "Test
Setup" below), were the frequency-invariance patch (on schedutil) is compared
to both non-invariant schedutil and active intel_pstate with powersave: all
three tested kernels behave the same performance-wise and with regard to power
consumption (performance per watt). The only notable difference is tbench:

comparison ratio of performance with baseline; 1.00 means neutral,
higher is better:

                      I_PSTATE      FREQ-INV
    ----------------------------------------
    tbench                1.04          1.05

performance-per-watt ratios with baseline; 1.00 means neutral, higher is better:

                      I_PSTATE      FREQ-INV
    ----------------------------------------
    tbench                1.03          1.04

which essentially means that frequency-invariant schedutil is 5% better than
baseline, the same as intel_pstate+powersave.

As the results above are averaged over the varying parameter, here the detailed
table.

Varying parameter  : number of clients
Unit               : MB/sec (higher is better)

                    5.2.0 vanilla (BASELINE)                 5.2.0 intel_pstate                     5.2.0 freq-inv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hmean   1         49.06  +- 2.12% (        )         51.66  +- 1.52% (   5.30%)         52.87  +- 0.88% (   7.76%)
Hmean   2         93.82  +- 0.45% (        )        103.24  +- 0.70% (  10.05%)        105.90  +- 0.70% (  12.88%)
Hmean   4        192.46  +- 1.15% (        )        215.95  +- 0.60% (  12.21%)        215.78  +- 1.43% (  12.12%)
Hmean   8        406.74  +- 2.58% (        )        438.58  +- 0.36% (   7.83%)        437.61  +- 0.97% (   7.59%)
Hmean   16       857.70  +- 1.22% (        )        890.26  +- 0.72% (   3.80%)        889.11  +- 0.73% (   3.66%)
Hmean   32      1760.10  +- 0.92% (        )       1791.70  +- 0.44% (   1.79%)       1787.95  +- 0.44% (   1.58%)
Hmean   64      3183.50  +- 0.34% (        )       3183.19  +- 0.36% (  -0.01%)       3187.53  +- 0.36% (   0.13%)
Hmean   128     4830.96  +- 0.31% (        )       4846.53  +- 0.30% (   0.32%)       4855.86  +- 0.30% (   0.52%)
Hmean   256     5467.98  +- 0.38% (        )       5793.80  +- 0.28% (   5.96%)       5821.94  +- 0.17% (   6.47%)
Hmean   512     5398.10  +- 0.06% (        )       5745.56  +- 0.08% (   6.44%)       5503.68  +- 0.07% (   1.96%)
Hmean   1024    5290.43  +- 0.63% (        )       5221.07  +- 0.47% (  -1.31%)       5277.22  +- 0.80% (  -0.25%)
Hmean   1088    5139.71  +- 0.57% (        )       5236.02  +- 0.71% (   1.87%)       5190.57  +- 0.41% (   0.99%)

2. NEUTRAL BENCHMARKS (ALL OTHERS)
----------------------------------

* pgbench (both read/write and read-only)
* NASA Parallel Benchmarks (NPB), MPI or OpenMP for message-passing
* hackbench
* netperf
* dbench
* kernbench
* gitsource (git unit test suite)

3. TEST SETUP
-------------

Test machine:

CPU Model   : Intel Xeon Phi CPU 7255 @ 1.10GHz (a.k.a. Knights Mill)
Fam/Mod/Ste : 6:133:0
Topology    : 1 socket, 68 cores / 272 threads
Memory      : 96G
Storage     : rotary, XFS filesystem

Max EFFICiency, BASE frequency and available turbo levels (MHz):

    EFFIC   1000 |**********
    BASE    1100 |***********
    68C     1100 |***********
    30C     1200 |************

Tested kernels:

Baseline      : v5.2,              intel_pstate passive,  schedutil
Comparison #1 : v5.2,              intel_pstate active ,  powersave
Comparison #2 : v5.2, this patch,  intel_pstate passive,  schedutil

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
---
 arch/x86/kernel/smpboot.c | 54 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

Comments

Peter Zijlstra Dec. 18, 2019, 8:22 p.m. UTC | #1
On Wed, Nov 13, 2019 at 01:46:51PM +0100, Giovanni Gherdovich wrote:
> The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
> accounting. On Xeon Phi CPUs set freq_max to the second-highest frequency
> reported by the CPU.
> 
> Xeon Phi CPUs such as Knights Landing and Knights Mill typically have either
> one or two turbo frequencies; in the former case that's 100 MHz above the base
> frequency, in the latter case the two levels are 100 MHz and 200 MHz above
> base frequency.
> 
> We set freq_max to the second-highest frequency reported by the CPU. This
> could be the base frequency (if only one turbo level is available) or the first
> turbo level (if two levels are available). The rationale is to compromise
> between power efficiency or performance -- going straight to max turbo would
> favor efficiency and blindly using base freq would favor performance.
> 
> For reference, this is how MSR_TURBO_RATIO_LIMIT must be parsed on a Xeon Phi
> to get the available frequencies (taken from a comment in turbostat's sources):
> 
>     [0] -- Reserved
>     [7:1] -- Base value of number of active cores of bucket 1.
>     [15:8] -- Base value of freq ratio of bucket 1.
>     [20:16] -- +ve delta of number of active cores of bucket 2.
>     i.e. active cores of bucket 2 =
>     active cores of bucket 1 + delta
>     [23:21] -- Negative delta of freq ratio of bucket 2.
>     i.e. freq ratio of bucket 2 =
>     freq ratio of bucket 1 - delta
>     [28:24]-- +ve delta of number of active cores of bucket 3.
>     [31:29]-- -ve delta of freq ratio of bucket 3.
>     [36:32]-- +ve delta of number of active cores of bucket 4.
>     [39:37]-- -ve delta of freq ratio of bucket 4.
>     [44:40]-- +ve delta of number of active cores of bucket 5.
>     [47:45]-- -ve delta of freq ratio of bucket 5.
>     [52:48]-- +ve delta of number of active cores of bucket 6.
>     [55:53]-- -ve delta of freq ratio of bucket 6.
>     [60:56]-- +ve delta of number of active cores of bucket 7.
>     [63:61]-- -ve delta of freq ratio of bucket 7.

Does it make sense to write a complete decoder and pass a @size
parameter just like the skx/glm case?

(I've no idea on the 4 I passed in, probably wants to be something else)

---
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
@@ -1863,36 +1863,12 @@ static const struct x86_cpu_id has_glm_t
 	{}
 };

-static int get_knl_turbo_ratio(u64 *turbo_ratio)
+static bool knl_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio, int size)
 {
+	int delta_cores, delta_fratio;
+	int cores, fratio;
+	int err, i;
 	u64 msr;
-	u32 ratio, delta_ratio;
-	int err, i, found = 0;
-
-	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &msr);
-	if (err)
-		return err;
-
-	ratio = (msr >> 8) & 0xFF;
-
-	for (i = 16; i < 64; i += 8) {
-		delta_ratio = (msr >> (i + 5)) & 0x7;
-		if (delta_ratio) {
-			*turbo_ratio = ratio - delta_ratio;
-			found = 1;
-			break;
-		}
-	}
-
-	if (!found)
-		return 1;
-
-	return 0;
-}
-
-static bool knl_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
-{
-	int err;

 	if (!x86_match_cpu(has_knl_turbo_ratio_limits))
 		return false;
@@ -1901,15 +1877,32 @@ static bool knl_set_cpu_max_freq(u64 *ra
 	if (err)
 		return false;

-	/* second highest turbo ratio */
-	err = get_knl_turbo_ratio(turbo_ratio);
+	*ratio = (*ratio >> 8) & 0xFF; /* max P state ratio */
+
+	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &msr);
 	if (err)
 		return false;

-	/* max P state ratio */
-	*ratio = (*ratio >> 8) & 0xFF;
+	cores = (msr >> 1) & 0x7F;
+	fratio = (msr >> 8) & 0xFF;

-	return true;
+	i = 16;
+	do {
+		if (cores >= size) {
+			*turbo_ratio = fratio;
+			return true;
+		}
+
+		delta_cores = (msr >> i) & 0x1F;
+		delta_fratio = (msr >> (i + 5)) & 0x07;
+
+		cores += delta_cores;
+		fratio -= delta_fratio;
+
+		i += 8;
+	} while (i < 64);
+
+	return false;
 }

 static bool skx_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio, int size)
@@ -1975,7 +1968,7 @@ static void intel_set_cpu_max_freq(void)
 	    skx_set_cpu_max_freq(&ratio, &turbo_ratio, 1))
 		goto set_value;

-	if (knl_set_cpu_max_freq(&ratio, &turbo_ratio))
+	if (knl_set_cpu_max_freq(&ratio, &turbo_ratio, 4))
 		goto set_value;

 	if (x86_match_cpu(has_skx_turbo_ratio_limits) &&
Giovanni Gherdovich Dec. 19, 2019, 8:32 p.m. UTC | #2
On Wed, 2019-12-18 at 21:22 +0100, Peter Zijlstra wrote:
> On Wed, Nov 13, 2019 at 01:46:51PM +0100, Giovanni Gherdovich wrote:
> > The scheduler needs the ratio freq_curr/freq_max for frequency-invariant
> > accounting. On Xeon Phi CPUs set freq_max to the second-highest frequency
> > reported by the CPU.
> > 
> > Xeon Phi CPUs such as Knights Landing and Knights Mill typically have either
> > one or two turbo frequencies; in the former case that's 100 MHz above the base
> > frequency, in the latter case the two levels are 100 MHz and 200 MHz above
> > base frequency.
> > 
> > We set freq_max to the second-highest frequency reported by the CPU. This
> > could be the base frequency (if only one turbo level is available) or the first
> > turbo level (if two levels are available). The rationale is to compromise
> > between power efficiency or performance -- going straight to max turbo would
> > favor efficiency and blindly using base freq would favor performance.
> > 
> > For reference, this is how MSR_TURBO_RATIO_LIMIT must be parsed on a Xeon Phi
> > to get the available frequencies (taken from a comment in turbostat's sources):
> > 
> >     [0] -- Reserved
> >     [7:1] -- Base value of number of active cores of bucket 1.
> >     [15:8] -- Base value of freq ratio of bucket 1.
> >     [20:16] -- +ve delta of number of active cores of bucket 2.
> >     i.e. active cores of bucket 2 =
> >     active cores of bucket 1 + delta
> >     [23:21] -- Negative delta of freq ratio of bucket 2.
> >     i.e. freq ratio of bucket 2 =
> >     freq ratio of bucket 1 - delta
> >     [28:24]-- +ve delta of number of active cores of bucket 3.
> >     [31:29]-- -ve delta of freq ratio of bucket 3.
> >     [36:32]-- +ve delta of number of active cores of bucket 4.
> >     [39:37]-- -ve delta of freq ratio of bucket 4.
> >     [44:40]-- +ve delta of number of active cores of bucket 5.
> >     [47:45]-- -ve delta of freq ratio of bucket 5.
> >     [52:48]-- +ve delta of number of active cores of bucket 6.
> >     [55:53]-- -ve delta of freq ratio of bucket 6.
> >     [60:56]-- +ve delta of number of active cores of bucket 7.
> >     [63:61]-- -ve delta of freq ratio of bucket 7.
> 
> Does it make sense to write a complete decoder and pass a @size
> parameter just like the skx/glm case?
> 
> (I've no idea on the 4 I passed in, probably wants to be something else)

I see your point: it's better to have a @size parameter so that if there is a
better value, we can easily change the number in the future. It also uniforms
to how the others are handled.

But from the little I've learned on Xeon Phi, the best parameter to
characterize the choice is not the @size of the buckets, but the number of
non-zero @delta's of freq ratio that you encounter while parsing the MSR.

The number of those non-zero freq ratio @delta's corresponds to how many freq
ratios you can have, and the documentation says this can be either 1 or 2. My
"documentation" is actually the 4-pages leaflet at [1], but I breafly asked
Len Brown and he said it made sense. So that's how I would parametrize the
code.

If I use your function, in order to extract the max_freq value I want from the
Xeon Phi machine I have, @size should be a number between 31 and 68 cores (see
example below). Not that there is anything wrong with 31 <= size <= 68, it's
just that I can make an assumption on how many freq ratios there are and
I'd like to do it.

My Xeon Phi test machine:

Xeon Phi CPU 7255 (Knights Mill)

    Max Efficiency:   1000 MHz
    Base Frequency:   1100 MHz
    68 cores turbo:   1100 MHz
    30 cores turbo:   1200 MHz

You can see the above has only 1 non-zero delta freq ratio; the base freq is
1100 MHz and max turbo is 1100+100 MHz.

If I could at least check a Knights Landing (which I don't have) and confirm
that 31 <= size gives me the second-highest freq ratio, I'd use your function,
but at the moment using @delta as a parameter seems safer.

[1] https://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/xeon-phi-processor-product-brief.pdf
---> footnote #3, last page:
   "Frequency listed is nominal (non-AVX) TDP frequency. For all-tile turbo
   frequency, add 100 MHz. For single-tile turbo frequency, add 200 MHz. For
   high-AVX instruction frequency, subtract 200 MHz."

Patch
diff mbox series

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 11d57d741584..0e79dcc03ae4 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1841,6 +1841,55 @@  static const struct x86_cpu_id has_glm_turbo_ratio_limits[] = {
 	{}
 };
 
+static int get_knl_turbo_ratio(u64 *turbo_ratio)
+{
+	u64 msr;
+	u32 ratio, delta_ratio;
+	int err, i, found = 0;
+
+	err = rdmsrl_safe(MSR_TURBO_RATIO_LIMIT, &msr);
+	if (err)
+		return err;
+
+	ratio = (msr >> 8) & 0xFF;
+
+	for (i = 16; i < 64; i += 8) {
+		delta_ratio = (msr >> (i + 5)) & 0x7;
+		if (delta_ratio) {
+			*turbo_ratio = ratio - delta_ratio;
+			found = 1;
+			break;
+		}
+	}
+
+	if (!found)
+		return 1;
+
+	return 0;
+}
+
+static bool knl_set_cpu_max_freq(u64 *ratio, u64 *turbo_ratio)
+{
+	int err;
+
+	if (!x86_match_cpu(has_knl_turbo_ratio_limits))
+		return false;
+
+	err = rdmsrl_safe(MSR_PLATFORM_INFO, ratio);
+	if (err)
+		return false;
+
+	/* second highest turbo ratio */
+	err = get_knl_turbo_ratio(turbo_ratio);
+	if (err)
+		return false;
+
+	/* max P state ratio */
+	*ratio = (*ratio >> 8) & 0xFF;
+
+	return true;
+}
+
 static int get_turbo_ratio_group(u64 *turbo_ratio)
 {
 	u64 ratio, core_counts;
@@ -1913,7 +1962,6 @@  static void intel_set_cpu_max_freq(void)
 	/*
 	 * TODO: add support for:
 	 *
-	 * - Xeon Phi (KNM, KNL)
 	 * - Atom Goldmont
 	 * - Atom Silvermont
 	 *
@@ -1923,10 +1971,12 @@  static void intel_set_cpu_max_freq(void)
 	u64 ratio = 1, turbo_ratio = 1;
 
 	if (turbo_disabled() ||
-		x86_match_cpu(has_knl_turbo_ratio_limits) ||
 		x86_match_cpu(has_glm_turbo_ratio_limits))
 		return;
 
+	if (knl_set_cpu_max_freq(&ratio, &turbo_ratio))
+		goto set_value;
+
 	if (skx_set_cpu_max_freq(&ratio, &turbo_ratio))
 		goto set_value;