[PATCH v6 19/21] x86/resctrl: Rename and change the units of resctrl_cqm_threshold

James Morse
2022-09-02T15:58:18Z

resctrl_cqm_threshold is stored in a hardware specific chunk size,
but exposed to user-space as bytes.

This means the filesystem parts of resctrl need to know how the hardware
counts, to convert the user provided byte value to chunks. The interface
between the architecture's resctrl code and the filesystem ought to
treat everything as bytes.

Change the unit of resctrl_cqm_threshold to bytes. resctrl_arch_rmid_read()
still returns its value in chunks, so this needs converting to bytes.
As all the users have been touched, rename the variable to
resctrl_rmid_realloc_threshold, which describes what the value is for.

Neither r->num_rmid nor hw_res->mon_scale are guaranteed to be a power
of 2, so the existing code introduces a rounding error from resctrl's
theoretical fraction of the cache usage. This behaviour is kept as it
ensures the user visible value matches the value read from hardware
when the rmid will be reallocated.

Reviewed-by: Jamie Iles <quic_jiles@quicinc.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v4:
* Added resctrl_arch_round_mon_val() to fix the user provided value.
* Keep the 'hw counts in chunks' comment.

Changes since v3:
* Preserved the rounding errors.
---
arch/x86/include/asm/resctrl.h | 9 ++++++
arch/x86/kernel/cpu/resctrl/internal.h | 1 -
arch/x86/kernel/cpu/resctrl/monitor.c | 43 ++++++++++++++++----------
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 9 ++----
include/linux/resctrl.h | 2 ++
5 files changed, 39 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index d60ed0668a59..d24b04ebf950 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -81,6 +81,15 @@ static void __resctrl_sched_in(void)
}
}

+static inline unsigned int resctrl_arch_round_mon_val(unsigned int val)
+{
+ unsigned int scale = boot_cpu_data.x86_cache_occ_scale;
+
+ /* h/w works in units of "boot_cpu_data.x86_cache_occ_scale" */
+ val /= scale;
+ return val * scale;
+}
+
static inline void resctrl_sched_in(void)
{
if (static_branch_likely(&rdt_enable_key))
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index bdb55c2fbdd3..c05e9b7cf77a 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -98,7 +98,6 @@ struct rmid_read {
u64 val;
};

-extern unsigned int resctrl_cqm_threshold;
extern bool rdt_alloc_capable;
extern bool rdt_mon_capable;
extern unsigned int rdt_mon_features;
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 27bb4947a176..e91afe99b763 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -17,7 +17,10 @@

#include <linux/module.h>
#include <linux/slab.h>
+
#include <asm/cpu_device_id.h>
+#include <asm/resctrl.h>
+
#include "internal.h"

struct rmid_entry {
@@ -37,8 +40,8 @@ static LIST_HEAD(rmid_free_lru);
* @rmid_limbo_count count of currently unused but (potentially)
* dirty RMIDs.
* This counts RMIDs that no one is currently using but that
- * may have a occupancy value > intel_cqm_threshold. User can change
- * the threshold occupancy value.
+ * may have a occupancy value > resctrl_rmid_realloc_threshold. User can
+ * change the threshold occupancy value.
*/
static unsigned int rmid_limbo_count;

@@ -59,10 +62,10 @@ bool rdt_mon_capable;
unsigned int rdt_mon_features;

/*
- * This is the threshold cache occupancy at which we will consider an
+ * This is the threshold cache occupancy in bytes at which we will consider an
* RMID available for re-allocation.
*/
-unsigned int resctrl_cqm_threshold;
+unsigned int resctrl_rmid_realloc_threshold;

#define CF(cf) ((unsigned long)(1048576 * (cf) + 0.5))

@@ -223,14 +226,13 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
*/
void __check_limbo(struct rdt_domain *d, bool force_free)
{
+ struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
+ struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
struct rmid_entry *entry;
- struct rdt_resource *r;
u32 crmid = 1, nrmid;
bool rmid_dirty;
u64 val = 0;

- r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
-
/*
* Skip RMID 0 and start from RMID 1 and check all the RMIDs that
* are marked as busy for occupancy < threshold. If the occupancy
@@ -245,10 +247,12 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
entry = __rmid_entry(nrmid);

if (resctrl_arch_rmid_read(r, d, entry->rmid,
- QOS_L3_OCCUP_EVENT_ID, &val))
+ QOS_L3_OCCUP_EVENT_ID, &val)) {
rmid_dirty = true;
- else
- rmid_dirty = (val >= resctrl_cqm_threshold);
+ } else {
+ val *= hw_res->mon_scale;
+ rmid_dirty = (val >= resctrl_rmid_realloc_threshold);
+ }

if (force_free || !rmid_dirty) {
clear_bit(entry->rmid, d->rmid_busy_llc);
@@ -289,13 +293,12 @@ int alloc_rmid(void)

static void add_rmid_to_limbo(struct rmid_entry *entry)
{
- struct rdt_resource *r;
+ struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
+ struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
struct rdt_domain *d;
int cpu, err;
u64 val = 0;

- r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
-
entry->busy = 0;
cpu = get_cpu();
list_for_each_entry(d, &r->domains, list) {
@@ -303,7 +306,8 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
err = resctrl_arch_rmid_read(r, d, entry->rmid,
QOS_L3_OCCUP_EVENT_ID,
&val);
- if (err || val <= resctrl_cqm_threshold)
+ val *= hw_res->mon_scale;
+ if (err || val <= resctrl_rmid_realloc_threshold)
continue;
}

@@ -744,6 +748,7 @@ int rdt_get_mon_l3_config(struct rdt_resource *r)
unsigned int mbm_offset = boot_cpu_data.x86_cache_mbm_width_offset;
struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
unsigned int cl_size = boot_cpu_data.x86_cache_size;
+ unsigned int threshold;
int ret;

hw_res->mon_scale = boot_cpu_data.x86_cache_occ_scale;
@@ -762,10 +767,14 @@ int rdt_get_mon_l3_config(struct rdt_resource *r)
*
* For a 35MB LLC and 56 RMIDs, this is ~1.8% of the LLC.
*/
- resctrl_cqm_threshold = cl_size * 1024 / r->num_rmid;
+ threshold = cl_size * 1024 / r->num_rmid;

- /* h/w works in units of "boot_cpu_data.x86_cache_occ_scale" */
- resctrl_cqm_threshold /= hw_res->mon_scale;
+ /*
+ * Because num_rmid may not be a power of two, round the value
+ * to the nearest multiple of hw_res->mon_scale so it matches a
+ * value the hardware will measure. mon_scale may not be a power of 2.
+ */
+ resctrl_rmid_realloc_threshold = resctrl_arch_round_mon_val(threshold);

ret = dom_data_init(r);
if (ret)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6c33dfe7ea53..849bdec37217 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1030,10 +1030,7 @@ static int rdt_delay_linear_show(struct kernfs_open_file *of,
static int max_threshold_occ_show(struct kernfs_open_file *of,
struct seq_file *seq, void *v)
{
- struct rdt_resource *r = of->kn->parent->priv;
- struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
-
- seq_printf(seq, "%u\n", resctrl_cqm_threshold * hw_res->mon_scale);
+ seq_printf(seq, "%u\n", resctrl_rmid_realloc_threshold);

return 0;
}
@@ -1055,7 +1052,6 @@ static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
- struct rdt_hw_resource *hw_res;
unsigned int bytes;
int ret;

@@ -1066,8 +1062,7 @@ static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
if (bytes > (boot_cpu_data.x86_cache_size * 1024))
return -EINVAL;

- hw_res = resctrl_to_arch_res(of->kn->parent->priv);
- resctrl_cqm_threshold = bytes / hw_res->mon_scale;
+ resctrl_rmid_realloc_threshold = resctrl_arch_round_mon_val(bytes);

return nbytes;
}
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 7ccfa0d1bb34..9995d043650a 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -250,4 +250,6 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d,
u32 rmid, enum resctrl_event_id eventid);

+extern unsigned int resctrl_rmid_realloc_threshold;
+
#endif /* _RESCTRL_H */
--
2.30.2