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x86/resctrl: Avoid redundant counter read in __mon_event_count()

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__mon_event_count() does the per-RMID, per-domain work for
user-initiated event count reads and the initialization of new monitor
groups.

In the initialization case, after resctrl_arch_reset_rmid() calls
__rmid_read() to record an initial count for a new monitor group, it
immediately calls resctrl_arch_rmid_read(). This re-read of the hardware
counter is unnecessary and the following computations are ignored by the
caller during initialization.

Following return from resctrl_arch_reset_rmid(), just clear the
mbm_state and return. This involves moving the mbm_state lookup into the
rr->first case, as it's not needed for regular event count reads: the
QOS_L3_OCCUP_EVENT_ID case was redundant with the accumulating logic at
the end of the function.

Signed-off-by: Peter Newman <peternewman@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/all/20221220164132.443083-2-peternewman%40google.com
This commit is contained in:
Peter Newman 2022-12-20 17:41:32 +01:00 committed by Dave Hansen
parent eeac8ede17
commit 322b72e0fd
1 changed files with 19 additions and 24 deletions
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43
arch/x86/kernel/cpu/resctrl/monitor.c
View File

@ -383,41 +383,36 @@ void free_rmid(u32 rmid)
list_add_tail(&entry->list, &rmid_free_lru);
}
static struct mbm_state *get_mbm_state(struct rdt_domain *d, u32 rmid,
enum resctrl_event_id evtid)
{
switch (evtid) {
case QOS_L3_MBM_TOTAL_EVENT_ID:
return &d->mbm_total[rmid];
case QOS_L3_MBM_LOCAL_EVENT_ID:
return &d->mbm_local[rmid];
default:
return NULL;
}
}
static int __mon_event_count(u32 rmid, struct rmid_read *rr)
{
struct mbm_state *m;
u64 tval = 0;
if (rr->first)
if (rr->first) {
resctrl_arch_reset_rmid(rr->r, rr->d, rmid, rr->evtid);
m = get_mbm_state(rr->d, rmid, rr->evtid);
if (m)
memset(m, 0, sizeof(struct mbm_state));
return 0;
}
rr->err = resctrl_arch_rmid_read(rr->r, rr->d, rmid, rr->evtid, &tval);
if (rr->err)
return rr->err;
switch (rr->evtid) {
case QOS_L3_OCCUP_EVENT_ID:
rr->val += tval;
return 0;
case QOS_L3_MBM_TOTAL_EVENT_ID:
m = &rr->d->mbm_total[rmid];
break;
case QOS_L3_MBM_LOCAL_EVENT_ID:
m = &rr->d->mbm_local[rmid];
break;
default:
/*
* Code would never reach here because an invalid
* event id would fail in resctrl_arch_rmid_read().
*/
return -EINVAL;
}
if (rr->first) {
memset(m, 0, sizeof(struct mbm_state));
return 0;
}
rr->val += tval;
return 0;