Re: [PATCH v9 4/9] x86/resctrl: Compute memory bandwidth for all supported events

["Luck, Tony" <tony.luck@intel.com>]

On Tue, Nov 19, 2024 at 07:45:01PM -0800, Reinette Chatre wrote:
> Hi Tony,
> 
> On 11/13/24 4:17 PM, Tony Luck wrote:
> > Computing the bandwidth for an event is cheap, and only done once
> > per second. Doing so simplifies switching between events and allows
> > choosing different events per ctrl_mon group.
> 
> This just reads like some a general statement. There surely can be
> some context, problem and *some* description about how this patch goes
> about addressing the problem?

I've rewritten this in the problem ... solution format.

> > 
> > Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
> > Signed-off-by: Tony Luck <tony.luck@intel.com>
> > ---
> >  arch/x86/kernel/cpu/resctrl/monitor.c | 72 ++++++++++++---------------
> >  1 file changed, 33 insertions(+), 39 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index 2176e355e864..da4ae21350c8 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -663,9 +663,12 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
> >   */
> >  static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr)
> >  {
> > -	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
> > -	struct mbm_state *m = &rr->d->mbm_local[idx];
> >  	u64 cur_bw, bytes, cur_bytes;
> > +	struct mbm_state *m;
> > +
> > +	m = get_mbm_state(rr->d, closid, rmid, rr->evtid);
> > +	if (WARN_ON_ONCE(!m))
> > +		return;
> >  
> >  	cur_bytes = rr->val;
> >  	bytes = cur_bytes - m->prev_bw_bytes;
> > @@ -826,54 +829,45 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_mon_domain *dom_mbm)
> >  	resctrl_arch_update_one(r_mba, dom_mba, closid, CDP_NONE, new_msr_val);
> >  }
> >  
> > -static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
> > -		       u32 closid, u32 rmid)
> > +static void mbm_update_one_event(struct rdt_resource *r, struct rdt_mon_domain *d,
> > +				 u32 closid, u32 rmid, enum resctrl_event_id evtid)
> >  {
> >  	struct rmid_read rr = {0};
> >  
> >  	rr.r = r;
> >  	rr.d = d;
> > +	rr.evtid = evtid;
> > +	rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> > +	if (IS_ERR(rr.arch_mon_ctx)) {
> > +		pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> > +				    PTR_ERR(rr.arch_mon_ctx));
> > +		return;
> > +	}
> > +
> > +	__mon_event_count(closid, rmid, &rr);
> >  
> >  	/*
> > -	 * This is protected from concurrent reads from user
> > -	 * as both the user and we hold the global mutex.
> > +	 * If the software controller is enabled, compute the
> > +	 * bandwidth for this event id.
> >  	 */
> > -	if (is_mbm_total_enabled()) {
> > -		rr.evtid = QOS_L3_MBM_TOTAL_EVENT_ID;
> > -		rr.val = 0;
> > -		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> > -		if (IS_ERR(rr.arch_mon_ctx)) {
> > -			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> > -					    PTR_ERR(rr.arch_mon_ctx));
> > -			return;
> > -		}
> > -
> > -		__mon_event_count(closid, rmid, &rr);
> > +	if (is_mba_sc(NULL))
> > +		mbm_bw_count(closid, rmid, &rr);
> >  
> > -		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> > -	}
> > -	if (is_mbm_local_enabled()) {
> > -		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
> > -		rr.val = 0;
> > -		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> > -		if (IS_ERR(rr.arch_mon_ctx)) {
> > -			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> > -					    PTR_ERR(rr.arch_mon_ctx));
> > -			return;
> > -		}
> > -
> > -		__mon_event_count(closid, rmid, &rr);
> > +	resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> > +}
> >  
> > -		/*
> > -		 * Call the MBA software controller only for the
> > -		 * control groups and when user has enabled
> > -		 * the software controller explicitly.
> > -		 */
> > -		if (is_mba_sc(NULL))
> > -			mbm_bw_count(closid, rmid, &rr);
> > +static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
> > +		       u32 closid, u32 rmid)
> > +{
> > +	/*
> > +	 * This is protected from concurrent reads from user
> > +	 * as both the user and we hold the global mutex.
> 
> I understand that you are just copy&pasting a comment here but could you please
> help to avoid any obstacles by removing the code impersonation? Perhaps something like:
> 
> 	 * This is protected from concurrent reads from user
> 	 * as both the user and overflow handler hold the global mutex.
> 
> (please feel free to improve)

No improvement to the text needed. But I did move some words from 2nd
line to the first to look better (IMHO).

> > +	 */
> > +	if (is_mbm_total_enabled())
> > +		mbm_update_one_event(r, d, closid, rmid, QOS_L3_MBM_TOTAL_EVENT_ID);
> >  
> > -		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> > -	}
> > +	if (is_mbm_local_enabled())
> > +		mbm_update_one_event(r, d, closid, rmid, QOS_L3_MBM_LOCAL_EVENT_ID);
> >  }
> >  
> >  /*
> 
> Reinette

-Tony