[PATCH v6 10/24] x86/resctrl: Allocate the cleanest CLOSID by searching closid_num_dirty_rmid

James Morse
2023-09-14T17:22:59Z

MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
used for different control groups.

This means once a CLOSID is allocated, all its monitoring ids may still be
dirty, and held in limbo.

Instead of allocating the first free CLOSID, on architectures where
CONFIG_RESCTRL_RMID_DEPENDS_ON_COSID is enabled, search
closid_num_dirty_rmid[] to find the cleanest CLOSID.

The CLOSID found is returned to closid_alloc() for the free list
to be updated.

Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-By: Peter Newman <peternewman@google.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v4:
* Dropped stale section from comment
---
arch/x86/kernel/cpu/resctrl/internal.h | 2 ++
arch/x86/kernel/cpu/resctrl/monitor.c | 42 ++++++++++++++++++++++++++
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++---
3 files changed, 58 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index ad6e874d9ed2..f06d3d3e0808 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -558,5 +558,7 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
void __init thread_throttle_mode_init(void);
void __init mbm_config_rftype_init(const char *config);
void rdt_staged_configs_clear(void);
+bool closid_allocated(unsigned int closid);
+int resctrl_find_cleanest_closid(void);

#endif /* _ASM_X86_RESCTRL_INTERNAL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 0c783301d106..0bbed8c62d42 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -388,6 +388,48 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
return ERR_PTR(-ENOSPC);
}

+/**
+ * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
+ * RMID are clean, or the CLOSID that has
+ * the most clean RMID.
+ *
+ * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
+ * may not be able to allocate clean RMID. To avoid this the allocator will
+ * choose the CLOSID with the most clean RMID.
+ *
+ * When the CLOSID and RMID are independent numbers, the first free CLOSID will
+ * be returned.
+ */
+int resctrl_find_cleanest_closid(void)
+{
+ u32 cleanest_closid = ~0, iter_num_dirty;
+ int i = 0;
+
+ lockdep_assert_held(&rdtgroup_mutex);
+
+ if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
+ return -EIO;
+
+ for (i = 0; i < closids_supported(); i++) {
+ if (closid_allocated(i))
+ continue;
+
+ iter_num_dirty = closid_num_dirty_rmid[i];
+ if (iter_num_dirty == 0)
+ return i;
+
+ if (cleanest_closid == ~0)
+ cleanest_closid = i;
+
+ if (iter_num_dirty < closid_num_dirty_rmid[cleanest_closid])
+ cleanest_closid = i;
+ }
+
+ if (cleanest_closid == ~0)
+ return -ENOSPC;
+ return cleanest_closid;
+}
+
/*
* For MPAM the RMID value is not unique, and has to be considered with
* the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index fa449ee0d1a7..1f8f1c417a4b 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -132,11 +132,20 @@ static void closid_init(void)

static int closid_alloc(void)
{
- u32 closid = ffs(closid_free_map);
+ u32 closid;
+ int err;

- if (closid == 0)
- return -ENOSPC;
- closid--;
+ if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
+ err = resctrl_find_cleanest_closid();
+ if (err < 0)
+ return err;
+ closid = err;
+ } else {
+ closid = ffs(closid_free_map);
+ if (closid == 0)
+ return -ENOSPC;
+ closid--;
+ }
clear_bit(closid, &closid_free_map);

return closid;
@@ -154,7 +163,7 @@ void closid_free(int closid)
* Return: true if @closid is currently associated with a resource group,
* false if @closid is free
*/
-static bool closid_allocated(unsigned int closid)
+bool closid_allocated(unsigned int closid)
{
return !test_bit(closid, &closid_free_map);
}
--
2.39.2