linux-kernel - Re: [PATCH v3 08/10] x86/resctrl: Add the sysfs interface to read the event configuration

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Date:   Fri, 26 Aug 2022 13:34:20 -0500
From:   "Moger, Babu" <babu.moger@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, fenghua.yu@...el.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     eranian@...gle.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, corbet@....net, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, bagasdotme@...il.com
Subject: Re: [PATCH v3 08/10] x86/resctrl: Add the sysfs interface to read the
 event configuration


On 8/26/22 12:34, Reinette Chatre wrote:
> Hi Babu,
>
> On 8/26/2022 9:49 AM, Moger, Babu wrote:
>> On 8/24/22 16:16, Reinette Chatre wrote:
>>> On 8/22/2022 6:44 AM, Babu Moger wrote:
> ...
>
>>>> +#define READS_TO_REMOTE_S_MEM		BIT(5)
>>>> +
>>>> +/* Dirty Victims to All Types of Memory */
>>>> +#define  DIRTY_VICTIS_TO_ALL_MEM	BIT(6)
>>> Is this intended to be "DIRTY_VICTIMS_TO_ALL_MEM" ?
>> Yes. that is what spec says.
> You did notice the typo, right?

oh. yea. Thanks


>
>>>> +	}
>>>> +
>>>> +	rdmsr(MSR_IA32_EVT_CFG_BASE + msr_index, md->u.mon_config, h);
>>>> +}
>>>> +
>>>> +void mondata_config_read(struct rdt_domain *d, union mon_data_bits *md)
>>>> +{
>>>> +	smp_call_function_any(&d->cpu_mask, mon_event_config_read, md, 1);
>>>> +}
>>>> +
>>>> +int rdtgroup_mondata_config_show(struct seq_file *m, void *arg)
>>>> +{
>>>> +	struct kernfs_open_file *of = m->private;
>>>> +	struct rdt_hw_resource *hw_res;
>>>> +	u32 resid, evtid, domid;
>>>> +	struct rdtgroup *rdtgrp;
>>>> +	struct rdt_resource *r;
>>>> +	union mon_data_bits md;
>>>> +	struct rdt_domain *d;
>>>> +	int ret = 0;
>>>> +
>>>> +	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>>>> +	if (!rdtgrp) {
>>>> +		ret = -ENOENT;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>> +	md.priv = of->kn->priv;
>>>> +	resid = md.u.rid;
>>>> +	domid = md.u.domid;
>>>> +	evtid = md.u.evtid;
>>>> +
>>>> +	hw_res = &rdt_resources_all[resid];
>>>> +	r = &hw_res->r_resctrl;
>>>> +
>>>> +	d = rdt_find_domain(r, domid, NULL);
>>>> +	if (IS_ERR_OR_NULL(d)) {
>>>> +		ret = -ENOENT;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>> +	mondata_config_read(d, &md);
>>>> +
>>>> +	seq_printf(m, "0x%x\n", md.u.mon_config);
>>> Looking at this patch and the next, the sysfs files are introduced to read
>>> from and write to the configuration register. From what I can tell the
>>> data is never used internally (what did I miss?). Why is the value of the
>>> configuration register stored? 
>> You didn't miss anything. We don't need to store it.  But we need it as
>> part of mon_data_bits structure because, it need to be passed to
>> mon_event_config_read and rdtgroup_mondata_config_write.
> These functions are introduced here ... so it is only needed because
> the demand is created here also. This can be changed, no? 

I think we can change that.


>
>> In these functions we need evtid and also config value (mon_config).
>>
> I see no need to pass evtid so deep - it can be checked right in
> rdtgroup_mondata_config_show() and then an appropriate wrapper
> can be called to just return the config value. Even if had to also
> pass evtid through many layers you could create a temporary structure
> to do so and not unnecessarily  increase the size of a long lived
> system structure to satisfy this temporary need.

Yea. I think we can do that. Let me try that.

Thanks

Babu

>
> Reinette

-- 
Thanks
Babu Moger