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

Reinette Chatre
2024-11-20T03:45:08Z

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?

>
> 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)

> + */
> + 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