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Date: Tue, 17 Jan 2023 19:10:33 +0000
From: "Yu, Fenghua" <fenghua.yu@...el.com>
To: James Morse <james.morse@....com>,
"x86@...nel.org" <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "Chatre, Reinette" <reinette.chatre@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
H Peter Anvin <hpa@...or.com>,
Babu Moger <Babu.Moger@....com>,
"shameerali.kolothum.thodi@...wei.com"
<shameerali.kolothum.thodi@...wei.com>,
D Scott Phillips OS <scott@...amperecomputing.com>,
"carl@...amperecomputing.com" <carl@...amperecomputing.com>,
"lcherian@...vell.com" <lcherian@...vell.com>,
"bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
"tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
"xingxin.hx@...nanolis.org" <xingxin.hx@...nanolis.org>,
"baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>,
"peternewman@...gle.com" <peternewman@...gle.com>
Subject: RE: [PATCH v2 07/18] x86/resctrl: Move CLOSID/RMID matching and
setting to use helpers
Hi, James,
> When switching tasks, the CLOSID and RMID that the new task should use are
> stored in struct task_struct. For x86 the CLOSID known by resctrl, the value in
> task_struct, and the value written to the CPU register are all the same thing.
>
> MPAM's CPU interface has two different PARTID's one for data accesses the
> other for instruction fetch. Storing resctrl's CLOSID value in struct task_struct
> implies the arch code knows whether resctrl is using CDP.
>
> Move the matching and setting of the struct task_struct properties to use
> helpers. This allows arm64 to store the hardware format of the register, instead
> of having to convert it each time.
>
> __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn
> values aren't seen as another CPU may schedule the task being moved while the
> value is being changed. MPAM has an additional corner-case here as the PMG
> bits extend the PARTID space. If the scheduler sees a new-CLOSID but old-RMID,
> the task will dirty an RMID that the limbo code is not watching causing an
> inaccurate count. x86's RMID are independent values, so the limbo code will still
> be watching the old-RMID in this circumstance.
> To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together.
> Both values must be provided together.
>
> Because MPAM's RMID values are not unique, the CLOSID must be provided
> when matching the RMID.
>
> CC: Valentin Schneider <vschneid@...hat.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> arch/x86/include/asm/resctrl.h | 18 ++++++++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 57 +++++++++++++++-----------
> 2 files changed, 51 insertions(+), 24 deletions(-)
>
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index 44d568f3577c..d589a82995ac 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -95,6 +95,24 @@ static inline unsigned int
> resctrl_arch_round_mon_val(unsigned int val)
> return val * scale;
> }
>
> +static inline void resctrl_arch_set_closid_rmid(struct task_struct *tsk,
> + u32 closid, u32 rmid)
> +{
> + WRITE_ONCE(tsk->closid, closid);
> + WRITE_ONCE(tsk->rmid, rmid);
> +}
> +
> +static inline bool resctrl_arch_match_closid(struct task_struct *tsk,
> +u32 closid) {
> + return READ_ONCE(tsk->closid) == closid; }
> +
> +static inline bool resctrl_arch_match_rmid(struct task_struct *tsk, u32 ignored,
> + u32 rmid)
> +{
> + return READ_ONCE(tsk->rmid) == rmid;
> +}
> +
> static inline void resctrl_sched_in(void) {
> if (static_branch_likely(&rdt_enable_key))
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index e1f879e13823..ced7400decae 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -84,7 +84,7 @@ void rdt_last_cmd_printf(const char *fmt, ...)
> *
> * Using a global CLOSID across all resources has some advantages and
> * some drawbacks:
> - * + We can simply set "current->closid" to assign a task to a resource
> + * + We can simply set current's closid to assign a task to a resource
> * group.
Seems this change doesn't gain anything. Maybe this change can be removed?
> * + Context switch code can avoid extra memory references deciding which
> * CLOSID to load into the PQR_ASSOC MSR
> @@ -549,14 +549,26 @@ static void update_task_closid_rmid(struct
> task_struct *t)
> _update_task_closid_rmid(t);
> }
>
> +static bool task_in_rdtgroup(struct task_struct *tsk, struct rdtgroup
> +*rdtgrp) {
> + u32 closid, rmid = rdtgrp->mon.rmid;
> +
> + if (rdtgrp->type == RDTCTRL_GROUP)
> + closid = rdtgrp->closid;
> + else if (rdtgrp->type == RDTMON_GROUP)
> + closid = rdtgrp->mon.parent->closid;
> + else
> + return false;
> +
> + return resctrl_arch_match_closid(tsk, closid) &&
> + resctrl_arch_match_rmid(tsk, closid, rmid); }
> +
> static int __rdtgroup_move_task(struct task_struct *tsk,
> struct rdtgroup *rdtgrp)
> {
> /* If the task is already in rdtgrp, no need to move the task. */
> - if ((rdtgrp->type == RDTCTRL_GROUP && tsk->closid == rdtgrp->closid
> &&
> - tsk->rmid == rdtgrp->mon.rmid) ||
> - (rdtgrp->type == RDTMON_GROUP && tsk->rmid == rdtgrp-
> >mon.rmid &&
> - tsk->closid == rdtgrp->mon.parent->closid))
> + if (task_in_rdtgroup(tsk, rdtgrp))
> return 0;
>
> /*
> @@ -567,19 +579,14 @@ static int __rdtgroup_move_task(struct task_struct
> *tsk,
> * For monitor groups, can move the tasks only from
> * their parent CTRL group.
> */
> -
> - if (rdtgrp->type == RDTCTRL_GROUP) {
> - WRITE_ONCE(tsk->closid, rdtgrp->closid);
> - WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
> - } else if (rdtgrp->type == RDTMON_GROUP) {
> - if (rdtgrp->mon.parent->closid == tsk->closid) {
> - WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
> - } else {
> - rdt_last_cmd_puts("Can't move task to different
> control group\n");
> - return -EINVAL;
> - }
> + if (rdtgrp->type == RDTMON_GROUP &&
> + !resctrl_arch_match_closid(tsk, rdtgrp->mon.parent->closid)) {
> + rdt_last_cmd_puts("Can't move task to different control
> group\n");
> + return -EINVAL;
> }
>
> + resctrl_arch_set_closid_rmid(tsk, rdtgrp->closid, rdtgrp->mon.rmid);
> +
> /*
> * Ensure the task's closid and rmid are written before determining if
> * the task is current that will decide if it will be interrupted.
> @@ -599,14 +606,15 @@ static int __rdtgroup_move_task(struct task_struct
> *tsk,
>
> static bool is_closid_match(struct task_struct *t, struct rdtgroup *r) {
> - return (rdt_alloc_capable &&
> - (r->type == RDTCTRL_GROUP) && (t->closid == r->closid));
> + return (rdt_alloc_capable && (r->type == RDTCTRL_GROUP) &&
> + resctrl_arch_match_closid(t, r->closid));
> }
>
> static bool is_rmid_match(struct task_struct *t, struct rdtgroup *r) {
> - return (rdt_mon_capable &&
> - (r->type == RDTMON_GROUP) && (t->rmid == r->mon.rmid));
> + return (rdt_mon_capable && (r->type == RDTMON_GROUP) &&
> + resctrl_arch_match_rmid(t, r->mon.parent->closid,
> + r->mon.rmid));
> }
>
> /**
> @@ -802,7 +810,7 @@ int proc_resctrl_show(struct seq_file *s, struct
> pid_namespace *ns,
> rdtg->mode != RDT_MODE_EXCLUSIVE)
> continue;
>
> - if (rdtg->closid != tsk->closid)
> + if (!resctrl_arch_match_closid(tsk, rdtg->closid))
> continue;
>
> seq_printf(s, "res:%s%s\n", (rdtg == &rdtgroup_default) ? "/" : "",
> @@ -810,7 +818,8 @@ int proc_resctrl_show(struct seq_file *s, struct
> pid_namespace *ns,
> seq_puts(s, "mon:");
> list_for_each_entry(crg, &rdtg->mon.crdtgrp_list,
> mon.crdtgrp_list) {
> - if (tsk->rmid != crg->mon.rmid)
> + if (!resctrl_arch_match_rmid(tsk, crg->mon.parent-
> >closid,
> + crg->mon.rmid))
> continue;
> seq_printf(s, "%s", crg->kn->name);
> break;
> @@ -2401,8 +2410,8 @@ static void rdt_move_group_tasks(struct rdtgroup
> *from, struct rdtgroup *to,
> for_each_process_thread(p, t) {
> if (!from || is_closid_match(t, from) ||
> is_rmid_match(t, from)) {
> - WRITE_ONCE(t->closid, to->closid);
> - WRITE_ONCE(t->rmid, to->mon.rmid);
> + resctrl_arch_set_closid_rmid(t, to->closid,
> + to->mon.rmid);
>
> /*
> * If the task is on a CPU, set the CPU in the mask.
> --
> 2.30.2
Thanks.
-Fenghua
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