RE: [PATCH v8 10/13] x86/resctrl: Add sysfs interface to write mbm_total_bytes_config

[Moger, Babu]

[AMD Official Use Only - General]

Hi Reinette,

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Sent: Tuesday, November 22, 2022 6:22 PM
> To: Moger, Babu <Babu.Moger@xxxxxxx>; corbet@xxxxxxx;
> tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; bp@xxxxxxxxx
> Cc: fenghua.yu@xxxxxxxxx; dave.hansen@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx;
> hpa@xxxxxxxxx; paulmck@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx;
> quic_neeraju@xxxxxxxxxxx; rdunlap@xxxxxxxxxxxxx;
> damien.lemoal@xxxxxxxxxxxxxxxxxx; songmuchun@xxxxxxxxxxxxx;
> peterz@xxxxxxxxxxxxx; jpoimboe@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> chang.seok.bae@xxxxxxxxx; pawan.kumar.gupta@xxxxxxxxxxxxxxx;
> jmattson@xxxxxxxxxx; daniel.sneddon@xxxxxxxxxxxxxxx; Das1, Sandipan
> <Sandipan.Das@xxxxxxx>; tony.luck@xxxxxxxxx; james.morse@xxxxxxx;
> linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> bagasdotme@xxxxxxxxx; eranian@xxxxxxxxxx
> Subject: Re: [PATCH v8 10/13] x86/resctrl: Add sysfs interface to write
> mbm_total_bytes_config
> 
> Hi Babu,
> 
> On 11/4/2022 1:01 PM, 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.
> >
> > The event configuration settings are domain specific and will affect
> > all the CPUs in the domain.
> >
> > 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@xxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/resctrl/rdtgroup.c |  130
> > ++++++++++++++++++++++++++++++++
> >  1 file changed, 129 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > index 18f9588a41cf..0cdccb69386e 100644
> > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > @@ -1505,6 +1505,133 @@ 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 = mon_event_config_index_get(mon_info->evtid);
> > +	if (index >= MAX_CONFIG_EVENTS) {
> > +		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(struct rdt_resource *r, struct rdt_domain *d,
> > +			    u32 evtid, u32 val)
> > +{
> > +	struct mon_config_info mon_info = {0};
> > +	int ret = 0;
> > +
> > +	rdt_last_cmd_clear();
> > +
> 
> Why is this extra clear() needed?

I am not sure why I added that. It does not seem required. I can remove it.
> 
> > +	/* 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 same then
> > +	 * we don't need to write it again.
> 
> Please no "we". Maybe just "If both are the same then no need to write it
> again."

Ok.

> 
> > +	 */
> > +	mon_info.evtid = evtid;
> > +	mondata_config_read(d, &mon_info);
> 
> Here I see motivation for doing validity check in mondata_config_read() as
> mentioned in feedback for patch #8. If hardware decides to use the other bits in
> that MSR then the check below would have trouble.
> 
> > +	if (mon_info.mon_config == val)
> > +		goto write_exit;
> > +
> 
> Could you please follow the custom in this area? Please see goto usage in the
> rest of the file that you are changing. The label should reflect the action being
> jumped to. In that sense, "write_exit" is not clear. A simple "goto out"
> would be clear and matches usage in rest of file.

Ok. Sure
> 
> > +	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);
> > +
> > +	/*
> > +	 * 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.
> > +	 */
> > +	memset(d->mbm_local, 0, sizeof(struct mbm_state) * r->num_rmid);
> > +	memset(d->mbm_total, 0, sizeof(struct mbm_state) * r->num_rmid);
> > +
> > +write_exit:
> > +	return ret;
> > +}
> > +
> > +static int mon_config_parse(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 (!dom_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("Missing '=' or non-numeric event
> configuration value\n");
> > +		return -EINVAL;
> > +	}
> 
> There is some duplication above ... both if () statememts check for "!dom_str" -
> is one intended to be "!id_str"?

The first check should be !id_str. Will correct it.

> Could both checks really mean that a "=" may be missing?

The second check failure means, there is a missing event configuration value. Will remove "missing =".

> 
> > +
> > +	list_for_each_entry(d, &r->domains, list) {
> > +		if (d->id == dom_id) {
> > +			ret = mbm_config_write(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_parse(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
> > +
> 
> The naming here does not reflect what is done ... much more than parsing is
> done here.
> 
> How about renaming mon_config_parse() to mon_config_write(), and
> renaming mon_config_write() to mon_config_write_domain() ?

Sure. Thanks
Babu

<<attachment: winmail.dat>>