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SubjectRE: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write mbm_total_bytes_config
Date
[AMD Official Use Only - General]

Hi Reinette,

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@intel.com>
> Sent: Thursday, December 15, 2022 12:25 PM
> To: Moger, Babu <Babu.Moger@amd.com>; corbet@lwn.net;
> tglx@linutronix.de; mingo@redhat.com; bp@alien8.de
> Cc: fenghua.yu@intel.com; dave.hansen@linux.intel.com; x86@kernel.org;
> hpa@zytor.com; paulmck@kernel.org; akpm@linux-foundation.org;
> quic_neeraju@quicinc.com; rdunlap@infradead.org;
> damien.lemoal@opensource.wdc.com; songmuchun@bytedance.com;
> peterz@infradead.org; jpoimboe@kernel.org; pbonzini@redhat.com;
> chang.seok.bae@intel.com; pawan.kumar.gupta@linux.intel.com;
> jmattson@google.com; daniel.sneddon@linux.intel.com; Das1, Sandipan
> <Sandipan.Das@amd.com>; tony.luck@intel.com; james.morse@arm.com;
> linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
> bagasdotme@gmail.com; eranian@google.com; christophe.leroy@csgroup.eu;
> jarkko@kernel.org; adrian.hunter@intel.com; quic_jiles@quicinc.com;
> peternewman@google.com
> Subject: Re: [PATCH v9 10/13] x86/resctrl: Add sysfs interface to write
> mbm_total_bytes_config
>
> Hi Babu,
>
> On 12/1/2022 7:37 AM, Babu Moger wrote:
> > The current event configuration for mbm_total_bytes can be changed by
> > the user by writing to the file
> > /sys/fs/resctrl/info/L3_MON/mbm_total_bytes_config.
>
> Please drop "current" from above
>
> >
> > The event configuration settings are domain specific and will affect
> > all the CPUs in the domain.
>
> please drop "will"
>
> >
> > Following are the types of events supported:
> >
> > ====
> ===========================================================
> > Bits Description
> > ====
> ===========================================================
> > 6 Dirty Victims from the QOS domain to all types of memory
> > 5 Reads to slow memory in the non-local NUMA domain
> > 4 Reads to slow memory in the local NUMA domain
> > 3 Non-temporal writes to non-local NUMA domain
> > 2 Non-temporal writes to local NUMA domain
> > 1 Reads to memory in the non-local NUMA domain
> > 0 Reads to memory in the local NUMA domain
> > ====
> ===========================================================
> >
> > For example:
> > To change the mbm_total_bytes to count only reads on domain 0, the
> > bits 0, 1, 4 and 5 needs to be set, which is 110011b (in hex 0x33).
> > Run the command.
> > $echo 0=0x33 > /sys/fs/resctrl/info/L3_MON/mbm_total_bytes_config
> >
> > To change the mbm_total_bytes to count all the slow memory reads on
> > domain 1, the bits 4 and 5 needs to be set which is 110000b (in hex 0x30).
> > Run the command.
> > $echo 1=0x30 > /sys/fs/resctrl/info/L3_MON/mbm_total_bytes_config
> >
> > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > ---
> > arch/x86/kernel/cpu/resctrl/monitor.c | 13 +++
> > arch/x86/kernel/cpu/resctrl/rdtgroup.c | 127
> ++++++++++++++++++++++++++++++++
> > include/linux/resctrl.h | 10 +++
> > 3 files changed, 149 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> > b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index 7c8a3a745041..b265856835de 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -176,6 +176,19 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r,
> struct rdt_domain *d,
> > memset(am, 0, sizeof(*am));
> > }
> >
> > +void resctrl_arch_reset_rmid_all(struct rdt_resource *r, struct
> > +rdt_domain *d) {
> > + struct rdt_hw_domain *hw_dom = resctrl_to_arch_dom(d);
> > +
> > + if (is_mbm_total_enabled())
> > + memset(hw_dom->arch_mbm_total, 0,
> > + sizeof(*hw_dom->arch_mbm_total) * r->num_rmid);
> > +
> > + if (is_mbm_local_enabled())
> > + memset(hw_dom->arch_mbm_local, 0,
> > + sizeof(*hw_dom->arch_mbm_local) * r->num_rmid); }
> > +
>
> We learned a lot more about this area after Peter's discovery:
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kern
> el.org%2Flkml%2F20221207112924.3602960-1-
> peternewman%40google.com%2F&amp;data=05%7C01%7Cbabu.moger%40am
> d.com%7Cc9ca23a7b3c643d2385508dadec9f83d%7C3dd8961fe4884e608e11a8
> 2d994e183d%7C0%7C0%7C638067256273943013%7CUnknown%7CTWFpbGZsb
> 3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%
> 3D%7C3000%7C%7C%7C&amp;sdata=Pmvi2L4L727GqALGaeEO0MbpcnuRcqKc
> opNNXuu%2BbFM%3D&amp;reserved=0
>
> Since this is a new generic function it should be clear in which scenarios it is
> valid.
> Could you please add a function comment that warns future developers about
> consequences if a new usage is considered? Something like:
>
> /*
> * Assumes that hardware counters are also reset and thus that there is no
> need
> * to record initial non-zero counts.
> */
>
> > static u64 mbm_overflow_count(u64 prev_msr, u64 cur_msr, unsigned int
> > width) {
> > u64 shift = 64 - width, chunks;
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > index 580f3cce19e2..8a22a652a6e8 100644
> > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > @@ -1517,6 +1517,130 @@ static int mbm_local_bytes_config_show(struct
> kernfs_open_file *of,
> > return 0;
> > }
> >
> > +static void mon_event_config_write(void *info) {
> > + struct mon_config_info *mon_info = info;
> > + u32 index;
> > +
>
> index does not need to be u32 ... mon_event_config_index_get() returns
> "unsigned int"
> and wrmsr expects "unsigned int", it can also just be "unsigned int".
>
>
> > + index = mon_event_config_index_get(mon_info->evtid);
> > + if (index == INVALID_CONFIG_INDEX) {
> > + pr_warn_once("Invalid event id %d\n", mon_info->evtid);
> > + return;
> > + }
> > + wrmsr(MSR_IA32_EVT_CFG_BASE + index, mon_info->mon_config, 0);
> }
> > +
> > +static int mbm_config_write_domain(struct rdt_resource *r,
> > + struct rdt_domain *d, u32 evtid, u32 val) {
> > + struct mon_config_info mon_info = {0};
> > + int ret = 0;
> > +
> > + /* mon_config cannot be more than the supported set of events */
> > + if (val > MAX_EVT_CONFIG_BITS) {
> > + rdt_last_cmd_puts("Invalid event configuration\n");
> > + return -EINVAL;
> > + }
> > +
> > + /*
> > + * Read the current config value first. If both are the same then
> > + * no need to write it again.
> > + */
> > + mon_info.evtid = evtid;
> > + mondata_config_read(d, &mon_info);
> > + if (mon_info.mon_config == val)
> > + goto out;
> > +
> > + mon_info.mon_config = val;
> > +
> > + /*
> > + * Update MSR_IA32_EVT_CFG_BASE MSRs on all the CPUs in the
> > + * domain. The MSRs offset from MSR MSR_IA32_EVT_CFG_BASE
> > + * are scoped at the domain level. Writing any of these MSRs
> > + * on one CPU is supposed to be observed by all CPUs in the
> > + * domain. However, the hardware team recommends to update
> > + * these MSRs on all the CPUs in the domain.
> > + */
> > + on_each_cpu_mask(&d->cpu_mask, mon_event_config_write,
> &mon_info,
> > +1);

Forgot about this. This snippet is going to change. I have tested and works fine.
How about this?

/*
* Update MSR_IA32_EVT_CFG_BASE MSR on one of the CPUs in the
* domain. The MSRs offset from MSR MSR_IA32_EVT_CFG_BASE
* are scoped at the domain level. Writing any of these MSRs
* on one CPU is supposed to be observed by all CPUs in the domain.
*/
smp_call_function_any(&d->cpu_mask, mon_event_config_write, &mon_info, 1);


/*
> + * Update MSR_IA32_EVT_CFG_BASE MSRs on all the CPUs in the
> + * domain. The MSRs offset from MSR MSR_IA32_EVT_CFG_BASE
> + * are scoped at the domain level. Writing any of these MSRs
> + * on one CPU is supposed to be observed by all CPUs in the
> + * domain. However, the hardware team recommends to update
> + * these MSRs on all the CPUs in the domain.
> + */
> + on_each_cpu_mask(&d->cpu_mask, mon_event_config_write, &mon_info, 1);


> > +
> > + /*
> > + * When an Event Configuration is changed, the bandwidth counters
> > + * for all RMIDs and Events will be cleared by the hardware. The
> > + * hardware also sets MSR_IA32_QM_CTR.Unavailable (bit 62) for
> > + * every RMID on the next read to any event for every RMID.
> > + * Subsequent reads will have MSR_IA32_QM_CTR.Unavailable (bit 62)
> > + * cleared while it is tracked by the hardware. Clear the
> > + * mbm_local and mbm_total counts for all the RMIDs.
> > + */
> > + resctrl_arch_reset_rmid_all(r, d);
>
> If I understand correctly the expectation is that when user space read counters
> (via mon_data files) right after the configuration was changed then this read
> will return "Unavailable" and then the next read will return data.
>
> If this is the case then I think a snippet about this user experience would be
> helpful to add to the documentation.
>
> Have you considered doing a preemptive read on the RMIDs that are in use to
> avoid users encountering "Unavailable"? I assume doing so on a busy system
> could potentially involve hundreds of register reads/writes.
>
> > +
> > +out:
> > + return ret;
> > +}
> > +
> > +static int mon_config_write(struct rdt_resource *r, char *tok, u32
> > +evtid) {
> > + char *dom_str = NULL, *id_str;
> > + unsigned long dom_id, val;
> > + struct rdt_domain *d;
> > + int ret = 0;
> > +
> > +next:
> > + if (!tok || tok[0] == '\0')
> > + return 0;
> > +
> > + /* Start processing the strings for each domain */
> > + dom_str = strim(strsep(&tok, ";"));
> > + id_str = strsep(&dom_str, "=");
> > +
> > + if (!id_str || kstrtoul(id_str, 10, &dom_id)) {
> > + rdt_last_cmd_puts("Missing '=' or non-numeric domain id\n");
> > + return -EINVAL;
> > + }
> > +
> > + if (!dom_str || kstrtoul(dom_str, 16, &val)) {
> > + rdt_last_cmd_puts("Non-numeric event configuration
> value\n");
> > + return -EINVAL;
> > + }
> > +
> > + list_for_each_entry(d, &r->domains, list) {
> > + if (d->id == dom_id) {
> > + ret = mbm_config_write_domain(r, d, evtid, val);
> > + if (ret)
> > + return -EINVAL;
> > + goto next;
> > + }
> > + }
> > +
> > + return -EINVAL;
> > +}
> > +
> > +static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
> > + char *buf, size_t nbytes,
> > + loff_t off)
> > +{
> > + struct rdt_resource *r = of->kn->parent->priv;
> > + int ret;
> > +
> > + /* Valid input requires a trailing newline */
> > + if (nbytes == 0 || buf[nbytes - 1] != '\n')
> > + return -EINVAL;
> > +
> > + cpus_read_lock();
> > + mutex_lock(&rdtgroup_mutex);
> > +
> > + rdt_last_cmd_clear();
> > +
> > + buf[nbytes - 1] = '\0';
> > +
> > + ret = mon_config_write(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
> > +
> > + mutex_unlock(&rdtgroup_mutex);
> > + cpus_read_unlock();
> > +
> > + return ret ?: nbytes;
> > +}
> > +
> > /* rdtgroup information files for one cache resource. */ static
> > struct rftype res_common_files[] = {
> > {
> > @@ -1617,9 +1741,10 @@ static struct rftype res_common_files[] = {
> > },
> > {
> > .name = "mbm_total_bytes_config",
> > - .mode = 0444,
> > + .mode = 0644,
> > .kf_ops = &rdtgroup_kf_single_ops,
> > .seq_show = mbm_total_bytes_config_show,
> > + .write = mbm_total_bytes_config_write,
> > },
> > {
> > .name = "mbm_local_bytes_config",
> > diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h index
> > 0cee154abc9f..e4dc65892446 100644
> > --- a/include/linux/resctrl.h
> > +++ b/include/linux/resctrl.h
> > @@ -250,6 +250,16 @@ 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);
> >
> > +/**
> > + * resctrl_arch_reset_rmid_all() - Reset any private state associated with
> > + * all the rmids.
>
> It could be more explicit:
> "Reset all private state associated with all rmids and eventids."
>
> > + * @r: The domain's resource.
> > + * @d: The rmid's domain.
>
> This copy&paste needs some changes to match this new utility.
> How about:
> @r: The resctrl resource.
> @d: The domain for which all architectural counter state will be cleared.
>
> I think it can be improved more but the above could be a start (please do not
> copy verbatim but ensure style is correct.)
>
> Keep in mind that this utility does not clear the non-architectural counter state.
> This does not apply to AMD since that state is used by the software controller,
> but it needs to be kept in mind if another usage for this utility arises.
>
> > + *
> > + * This can be called from any CPU.
> > + */
> > +void resctrl_arch_reset_rmid_all(struct rdt_resource *r, struct
> > +rdt_domain *d);
> > +
> > extern unsigned int resctrl_rmid_realloc_threshold; extern unsigned
> > int resctrl_rmid_realloc_limit;
> >
> >
> >
>
> The above hunk fails the "no spaces before tabs" checkpatch check.
>
> Reinette

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