Date:   Wed, 26 Oct 2022 14:52:44 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     fenghua.yu@...el.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, paulmck@...nel.org, akpm@...ux-foundation.org,
        quic_neeraju@...cinc.com, rdunlap@...radead.org,
        damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
        peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
        chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
        jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
        sandipan.das@....com, tony.luck@...el.com, james.morse@....com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        bagasdotme@...il.com, eranian@...gle.com
Subject: Re: [PATCH v7 09/12] x86/resctrl: Add sysfs interface to write
 mbm_total_bytes event configuration

Hi Reinette,


On 10/25/22 18:48, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/17/2022 3:27 PM, Babu Moger wrote:
>> The current event configuration can be changed by the user by writing
>> to the configuration file /sys/fs/resctrl/info/L3_MON/mbm_total_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_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_config
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>>  arch/x86/kernel/cpu/resctrl/internal.h |   23 +++++
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |  146 ++++++++++++++++++++++++++++++++
>>  2 files changed, 169 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>> index 326a1b582f38..c42b12934a0e 100644
>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>> @@ -42,6 +42,29 @@
>>   */
>>  #define MBM_CNTR_WIDTH_OFFSET_MAX (62 - MBM_CNTR_WIDTH_BASE)
>>  
>> +/* Reads to Local DRAM Memory */
>> +#define READS_TO_LOCAL_MEM             BIT(0)
>> +
>> +/* Reads to Remote DRAM Memory */
>> +#define READS_TO_REMOTE_MEM            BIT(1)
>> +
>> +/* Non-Temporal Writes to Local Memory */
>> +#define NON_TEMP_WRITE_TO_LOCAL_MEM    BIT(2)
>> +
>> +/* Non-Temporal Writes to Remote Memory */
>> +#define NON_TEMP_WRITE_TO_REMOTE_MEM   BIT(3)
>> +
>> +/* Reads to Local Memory the system identifies as "Slow Memory" */
>> +#define READS_TO_LOCAL_S_MEM           BIT(4)
>> +
>> +/* Reads to Remote Memory the system identifies as "Slow Memory" */
>> +#define READS_TO_REMOTE_S_MEM          BIT(5)
>> +
>> +/* Dirty Victims to All Types of Memory */
>> +#define  DIRTY_VICTIMS_TO_ALL_MEM      BIT(6)
>> +
>> +/* Max event bits supported */
>> +#define MAX_EVT_CONFIG_BITS            GENMASK(6, 0)
>>  
>>  struct rdt_fs_context {
>>  	struct kernfs_fs_context	kfc;
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 305fb0475970..25ff56ecb817 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -1494,6 +1494,151 @@ static int mbm_local_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 msr_index;
>> +
>> +	switch (mon_info->evtid) {
>> +	case QOS_L3_MBM_TOTAL_EVENT_ID:
>> +		msr_index = 0;
>> +		break;
>> +	case QOS_L3_MBM_LOCAL_EVENT_ID:
>> +		msr_index = 1;
>> +		break;
>> +	default:
>> +		/* Not expected to come here */
>> +		return;
>> +	}
>> +
>> +	wrmsr(MSR_IA32_EVT_CFG_BASE + msr_index, mon_info->mon_config, 0);
>> +}
> This duplicates most of mon_event_config_read() from earlier patch. Would a
> utility like "mon_event_config_index_get()" help here?
Yes. We can do that.
>
>> +
>> +static int mbm_config_write(struct rdt_resource *r, struct rdt_domain *d,
>> +			    u32 evtid, u32 val)
>> +{
>> +	struct mon_config_info mon_info = {0};
>> +	cpumask_var_t cpu_mask;
>> +	int ret = 0, cpu;
>> +
>> +	rdt_last_cmd_clear();
>> +
>> +	/* 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;
>> +	}
>> +
>> +	cpus_read_lock();
>> +
>> +	if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL)) {
>> +		rdt_last_cmd_puts("cpu_mask allocation failed\n");
>> +		ret = -ENOMEM;
>> +		goto e_unlock;
>> +	}
>> +
>> +	/*
>> +	 * Read the current config value first. If both are same then
>> +	 * we dont need to write it again.
> "we dont need" -> "we don't need"
Sure.
>
>> +	 */
>> +	mon_info.evtid = evtid;
>> +	mondata_config_read(d, &mon_info);
>> +	if (mon_info.mon_config == val)
>> +		goto e_cpumask;
>> +
>> +	mon_info.mon_config = val;
>> +
>> +	/* Pick all the CPUs in the domain instance */
>> +	for_each_cpu(cpu, &d->cpu_mask)
>> +		cpumask_set_cpu(cpu, cpu_mask);
>> +
> Why is it necessary to create a new CPU mask just to populate it
> with all CPUs in another CPU mask? Why not just use the original CPU mask?

I thought convention was to create a new mask when calling on_each_cpu_mask().

But, I dont see that requirement. I can use d->cpu_mask for this directly.

>
>> +	/*
>> +	 * Update MSR_IA32_EVT_CFG_BASE MSRs on all the CPUs in
>> +	 * cpu_mask. 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(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);
>> +
>> +e_cpumask:
>> +	free_cpumask_var(cpu_mask);
>> +
>> +e_unlock:
>> +	cpus_read_unlock();
>> +
>> +	return ret;
>> +}
>> +
>> +static int mon_config_parse(struct rdt_resource *r, char *tok, u32 evtid)
>> +{
>> +	char *dom_str = NULL, *id_str;
>> +	struct rdt_domain *d;
>> +	unsigned long dom_id, val;
> Please use reverse fir tree order.
Sure.
>
>> +	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;
>> +	}
>> +
>> +	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_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;
>> +
>> +	rdt_last_cmd_clear();
>> +
> How is this code protected from interference by other actions? Needs rdtgroup_mutex?

Yes. Sure.

Thanks

Babu

>
>> +	buf[nbytes - 1] = '\0';
>> +
>> +	ret = mon_config_parse(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
>> +
>> +	return ret ?: nbytes;
>> +}
>> +
>>  /* rdtgroup information files for one cache resource. */
>>  static struct rftype res_common_files[] = {
>>  	{
>> @@ -1597,6 +1742,7 @@ static struct rftype res_common_files[] = {
>>  		.mode		= 0644,
>>  		.kf_ops		= &rdtgroup_kf_single_ops,
>>  		.seq_show	= mbm_total_config_show,
>> +		.write		= mbm_total_config_write,
>>  	},
>>  	{
>>  		.name		= "mbm_local_config",
>>
>>
> Reinette

-- 
Thanks
Babu Moger

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