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Subject[PATCH] x86/resctrl: Correct MBM total and local values
Date
MBM total and local readings are corrected by the following correction
factor table on Broadwell server and Skylake server.

core rmid rmid correction
count count threshold factor
1 8 0 1.000000
2 16 0 1.000000
3 24 15 0.969650
4 32 0 1.000000
5 40 31 1.066667
6 48 31 0.969650
7 56 47 1.142857
8 64 0 1.000000
9 72 63 1.185115
10 80 63 1.066553
11 88 79 1.454545
12 96 0 1.000000
13 104 95 1.230769
14 112 95 1.142857
15 120 95 1.066667
16 128 0 1.000000
17 136 127 1.254863
18 144 127 1.185255
19 152 0 1.000000
20 160 127 1.066667
21 168 0 1.000000
22 176 159 1.454334
23 184 0 1.000000
24 192 127 0.969744
25 200 191 1.280246
26 208 191 1.230921
27 216 0 1.000000
28 224 191 1.143118

If rmid > rmid threshold, MBM total and local values should be multipled
by the correction factor.

The above table is modified for better code:
1. The threshold 0 is changed to rmid count - 1 so we don't do correction
for the case.
2. Correction factor is normalized to 2^20 for better performance
by avoiding floating point and division calculation in corrected
MBM values.

Detailed information about the correction is described in erratum SKX99:
https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html
and BDF102: https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e5-v4-spec-update.pdf

The problem is described in details in "3.6 Intel MBM RMID Imbalance":
https://software.intel.com/content/www/us/en/develop/articles/intel-resource-director-technology-rdt-reference-manual.html

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---

Applied to tip:x86/cache.

arch/x86/kernel/cpu/resctrl/core.c | 4 ++
arch/x86/kernel/cpu/resctrl/internal.h | 1 +
arch/x86/kernel/cpu/resctrl/monitor.c | 75 +++++++++++++++++++++++++-
3 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9e1712e8aef7..efe3ed61ae0c 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -893,6 +893,10 @@ static __init void __check_quirks_intel(void)
set_rdt_options("!cmt,!mbmtotal,!mbmlocal,!l3cat");
else
set_rdt_options("!l3cat");
+ /* FALLTHROUGH */
+ case INTEL_FAM6_BROADWELL_X:
+ intel_rdt_mbm_quirk();
+ break;
}
}

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 80fa997fae60..0be0232ac03a 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -616,6 +616,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
void mbm_setup_overflow_handler(struct rdt_domain *dom,
unsigned long delay_ms);
void mbm_handle_overflow(struct work_struct *work);
+void intel_rdt_mbm_quirk(void);
bool is_mba_sc(struct rdt_resource *r);
void setup_default_ctrlval(struct rdt_resource *r, u32 *dc, u32 *dm);
u32 delay_bw_map(unsigned long bw, struct rdt_resource *r);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 54dffe574e67..05e06744e4b1 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -18,6 +18,7 @@
#include <linux/module.h>
#include <linux/slab.h>
#include <asm/cpu_device_id.h>
+#include <asm/intel-family.h>
#include "internal.h"

struct rmid_entry {
@@ -64,6 +65,61 @@ unsigned int rdt_mon_features;
*/
unsigned int resctrl_cqm_threshold;

+#define CF(cf) ((unsigned long)(1048576 * (cf) + 0.5))
+
+/*
+ * MBM total and local correction table indexed by CBO which is equal to
+ * (x86_cache_max_rmid + 1) / 8 - 1 and is from 0 up to 27.
+ * The correction factor is normalized to 2^20 (1048576) so it's faster
+ * to calculate corrected value by shifting:
+ * corrected_value = (original_value * correction_factor) >> 20
+ */
+static struct mbm_creation_factor_table {
+ u32 rmidthreshold;
+ u64 cf;
+} mbm_cf_table[] = {
+ {7, CF(1.000000)},
+ {15, CF(1.000000)},
+ {15, CF(0.969650)},
+ {31, CF(1.000000)},
+ {31, CF(1.066667)},
+ {31, CF(0.969650)},
+ {47, CF(1.142857)},
+ {63, CF(1.000000)},
+ {63, CF(1.185115)},
+ {63, CF(1.066553)},
+ {79, CF(1.454545)},
+ {95, CF(1.000000)},
+ {95, CF(1.230769)},
+ {95, CF(1.142857)},
+ {95, CF(1.066667)},
+ {127, CF(1.000000)},
+ {127, CF(1.254863)},
+ {127, CF(1.185255)},
+ {151, CF(1.000000)},
+ {127, CF(1.066667)},
+ {167, CF(1.000000)},
+ {159, CF(1.454334)},
+ {183, CF(1.000000)},
+ {127, CF(0.969744)},
+ {191, CF(1.280246)},
+ {191, CF(1.230921)},
+ {215, CF(1.000000)},
+ {191, CF(1.143118)},
+};
+
+static u32 mbm_cf_rmidthreshold = UINT_MAX;
+static u64 mbm_cf;
+
+static inline u64 corrected_mbm_count(u32 rmid, unsigned long val)
+{
+ /* Correct MBM value. */
+ if (rmid > mbm_cf_rmidthreshold)
+ val = (val * mbm_cf) >> 20;
+
+ return val;
+}
+
static inline struct rmid_entry *__rmid_entry(u32 rmid)
{
struct rmid_entry *entry;
@@ -260,7 +316,8 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
m->chunks += chunks;
m->prev_msr = tval;

- rr->val += m->chunks;
+ rr->val += corrected_mbm_count(rmid, m->chunks);
+
return 0;
}

@@ -280,7 +337,7 @@ static void mbm_bw_count(u32 rmid, struct rmid_read *rr)

chunks = mbm_overflow_count(m->prev_bw_msr, tval, rr->r->mbm_width);
m->chunks += chunks;
- cur_bw = (chunks * r->mon_scale) >> 20;
+ cur_bw = (corrected_mbm_count(rmid, chunks) * r->mon_scale) >> 20;

if (m->delta_comp)
m->delta_bw = abs(cur_bw - m->prev_bw);
@@ -644,3 +701,17 @@ int rdt_get_mon_l3_config(struct rdt_resource *r)

return 0;
}
+
+void intel_rdt_mbm_quirk(void)
+{
+ int cf_index;
+
+ cf_index = (boot_cpu_data.x86_cache_max_rmid + 1) / 8 - 1;
+ if (cf_index >= ARRAY_SIZE(mbm_cf_table)) {
+ pr_info("No MBM correction factor available\n");
+ return;
+ }
+
+ mbm_cf_rmidthreshold = mbm_cf_table[cf_index].rmidthreshold;
+ mbm_cf = mbm_cf_table[cf_index].cf;
+}
--
2.28.0
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