Messages in this thread Patch in this message | | | From | James Morse <> | Subject | [PATCH v3 10/19] x86/resctrl: Allow resctrl_arch_rmid_read() to sleep | Date | Mon, 20 Mar 2023 17:26:11 +0000 |
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MPAM's cache occupancy counters can take a little while to settle once the monitor has been configured. The maximum settling time is described to the driver via a firmware table. The value could be large enough that it makes sense to sleep.
To avoid exposing this to resctrl, it should be hidden behind MPAM's resctrl_arch_rmid_read(). But add_rmid_to_limbo() calls resctrl_arch_rmid_read() from a non-preemptible context.
add_rmid_to_limbo() is opportunistically reading the L3 occupancy counter on this domain to avoid adding the RMID to limbo if this domain's value has drifted below resctrl_rmid_realloc_threshold since the limbo handler last ran. Determining 'this domain' involves disabling preeption to prevent the thread being migrated to CPUs in a different domain between the check and resctrl_arch_rmid_read() call. The check is skipped for all remote domains.
Instead, call resctrl_arch_rmid_read() for each domain, and get it to read the arch specific counter via IPI if its called on a CPU outside the target domain. By covering remote domains, this change stops the limbo handler from being started unnecessarily if a remote domain is below the threshold.
This also allows resctrl_arch_rmid_read() to sleep.
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com> Signed-off-by: James Morse <james.morse@arm.com> --- The alternative is to remove the counter read from this path altogether, and assume user-space would never try to re-allocate the last RMID before the limbo handler runs next. --- arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 12 +----- arch/x86/kernel/cpu/resctrl/monitor.c | 48 +++++++++++++++-------- 2 files changed, 33 insertions(+), 27 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c index b06e86839d00..9161bc95eea7 100644 --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c @@ -543,16 +543,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r, rr->val = 0; rr->first = first; - cpu = get_cpu(); - if (cpumask_test_cpu(cpu, &d->cpu_mask)) { - mon_event_count(rr); - put_cpu(); - } else { - put_cpu(); - - cpu = cpumask_any_housekeeping(&d->cpu_mask); - smp_call_on_cpu(cpu, mon_event_count, rr, false); - } + cpu = cpumask_any_housekeeping(&d->cpu_mask); + smp_call_on_cpu(cpu, mon_event_count, rr, false); } int rdtgroup_mondata_show(struct seq_file *m, void *arg) diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c index 5e9e876c3409..de72df06b37b 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -253,22 +253,42 @@ static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int width) return chunks >> shift; } +struct __rmid_read_arg +{ + u32 rmid; + enum resctrl_event_id eventid; + + u64 msr_val; + int err; +}; + +static void smp_call_rmid_read(void *_arg) +{ + struct __rmid_read_arg *arg = _arg; + + arg->err = __rmid_read(arg->rmid, arg->eventid, &arg->msr_val); +} + int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d, u32 closid, u32 rmid, enum resctrl_event_id eventid, u64 *val) { struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r); struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d); + struct __rmid_read_arg arg; struct arch_mbm_state *am; u64 msr_val, chunks; - int ret; + int err; - if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask)) - return -EINVAL; + arg.rmid = rmid; + arg.eventid = eventid; - ret = __rmid_read(rmid, eventid, &msr_val); - if (ret) - return ret; + err = smp_call_function_any(&d->cpu_mask, smp_call_rmid_read, &arg, true); + if (err) + return err; + if (arg.err) + return arg.err; + msr_val = arg.msr_val; am = get_arch_mbm_state(hw_dom, rmid, eventid); if (am) { @@ -424,23 +444,18 @@ static void add_rmid_to_limbo(struct rmid_entry *entry) { struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl; struct rdt_domain *d; - int cpu, err; u64 val = 0; u32 idx; + int err; idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid); entry->busy = 0; - cpu = get_cpu(); list_for_each_entry(d, &r->domains, list) { - if (cpumask_test_cpu(cpu, &d->cpu_mask)) { - err = resctrl_arch_rmid_read(r, d, entry->closid, - entry->rmid, - QOS_L3_OCCUP_EVENT_ID, - &val); - if (err || val <= resctrl_rmid_realloc_threshold) - continue; - } + err = resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid, + QOS_L3_OCCUP_EVENT_ID, &val); + if (err || val <= resctrl_rmid_realloc_threshold) + continue; /* * For the first limbo RMID in the domain, @@ -451,7 +466,6 @@ static void add_rmid_to_limbo(struct rmid_entry *entry) set_bit(idx, d->rmid_busy_llc); entry->busy++; } - put_cpu(); if (entry->busy) rmid_limbo_count++; -- 2.39.2
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