Re: [PATCH v7 09/12] x86/resctrl: Add sysfs interface to write mbm_total_bytes event configuration

[Reinette Chatre]

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@xxxxxxx>
> ---
>  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?

> +
> +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"

> +	 */
> +	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?

> +	/*
> +	 * 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.

> +	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?

> +	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