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Message-ID: <7e611640-9e7a-42a1-b0d7-f8b76999e9b2@amd.com>
Date: Thu, 9 Nov 2023 14:47:55 -0600
From: "Moger, Babu" <babu.moger@....com>
To: James Morse <james.morse@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>,
Reinette Chatre <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>,
shameerali.kolothum.thodi@...wei.com,
D Scott Phillips OS <scott@...amperecomputing.com>,
carl@...amperecomputing.com, lcherian@...vell.com,
bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v7 16/24] x86/resctrl: Make resctrl_mounted checks
explicit
On 10/25/23 13:03, James Morse wrote:
> The rdt_enable_key is switched when resctrl is mounted, and used to
> prevent a second mount of the filesystem. It also enables the
> architecture's context switch code.
>
> This requires another architecture to have the same set of static-keys,
> as resctrl depends on them too. The existing users of these static-keys
> are implicitly also checking if the filesystem is mounted.
>
> Make the resctrl_mounted checks explicit: resctrl can keep track of
> whether it has been mounted once. This doesn't need to be combined with
> whether the arch code is context switching the CLOSID.
>
> rdt_mon_enable_key is never used just to test that resctrl is mounted,
> but does also have this implication. Add a resctrl_mounted to all uses
> of rdt_mon_enable_key. This will allow rdt_mon_enable_key to be swapped
> with a helper in a subsequent patch.
>
> This will allow the static-key changing to be moved behind resctrl_arch_
> calls.
>
> Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: James Morse <james.morse@....com>
Reviewed-by: Babu Moger <babu.moger@....com>
>
> ---
> Changes since v3:
> * Removed a newline.
> * Rephrased commit message
>
> Changes since v4:
> * Rephrased comment.
>
> No changes since v6
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 1 +
> arch/x86/kernel/cpu/resctrl/monitor.c | 12 ++++++++++--
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 23 +++++++++++++++++------
> 3 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index bb07b9b01e36..5ce49503fcd8 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -145,6 +145,7 @@ extern bool rdt_alloc_capable;
> extern bool rdt_mon_capable;
> extern unsigned int rdt_mon_features;
> extern struct list_head resctrl_schema_all;
> +extern bool resctrl_mounted;
>
> enum rdt_group_type {
> RDTCTRL_GROUP = 0,
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 1ca8db8c82cc..843df6f64e0e 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -837,7 +837,11 @@ void mbm_handle_overflow(struct work_struct *work)
>
> mutex_lock(&rdtgroup_mutex);
>
> - if (!static_branch_likely(&rdt_mon_enable_key))
> + /*
> + * If the filesystem has been unmounted this work no longer needs to
> + * run.
> + */
> + if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
> goto out_unlock;
>
> r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> @@ -870,7 +874,11 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
> unsigned long delay = msecs_to_jiffies(delay_ms);
> int cpu;
>
> - if (!static_branch_likely(&rdt_mon_enable_key))
> + /*
> + * When a domain comes online there is no guarantee the filesystem is
> + * mounted. If not, there is no need to catch counter overflow.
> + */
> + if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
> return;
> cpu = cpumask_any_housekeeping(&dom->cpu_mask);
> dom->mbm_work_cpu = cpu;
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index fe6dfea471f2..9ce1f981c8e1 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -42,6 +42,9 @@ LIST_HEAD(rdt_all_groups);
> /* list of entries for the schemata file */
> LIST_HEAD(resctrl_schema_all);
>
> +/* The filesystem can only be mounted once. */
> +bool resctrl_mounted;
> +
> /* Kernel fs node for "info" directory under root */
> static struct kernfs_node *kn_info;
>
> @@ -881,7 +884,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
> mutex_lock(&rdtgroup_mutex);
>
> /* Return empty if resctrl has not been mounted. */
> - if (!static_branch_unlikely(&rdt_enable_key)) {
> + if (!resctrl_mounted) {
> seq_puts(s, "res:\nmon:\n");
> goto unlock;
> }
> @@ -2613,7 +2616,7 @@ static int rdt_get_tree(struct fs_context *fc)
> /*
> * resctrl file system can only be mounted once.
> */
> - if (static_branch_unlikely(&rdt_enable_key)) {
> + if (resctrl_mounted) {
> ret = -EBUSY;
> goto out;
> }
> @@ -2674,8 +2677,10 @@ static int rdt_get_tree(struct fs_context *fc)
> if (rdt_mon_capable)
> static_branch_enable_cpuslocked(&rdt_mon_enable_key);
>
> - if (rdt_alloc_capable || rdt_mon_capable)
> + if (rdt_alloc_capable || rdt_mon_capable) {
> static_branch_enable_cpuslocked(&rdt_enable_key);
> + resctrl_mounted = true;
> + }
>
> if (is_mbm_enabled()) {
> r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> @@ -2949,6 +2954,7 @@ static void rdt_kill_sb(struct super_block *sb)
> static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
> static_branch_disable_cpuslocked(&rdt_mon_enable_key);
> static_branch_disable_cpuslocked(&rdt_enable_key);
> + resctrl_mounted = false;
> kernfs_kill_sb(sb);
> mutex_unlock(&rdtgroup_mutex);
> cpus_read_unlock();
> @@ -3918,7 +3924,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
> * If resctrl is mounted, remove all the
> * per domain monitor data directories.
> */
> - if (static_branch_unlikely(&rdt_mon_enable_key))
> + if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
> rmdir_mondata_subdir_allrdtgrp(r, d->id);
>
> if (is_mbm_enabled())
> @@ -3995,8 +4001,13 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
> if (is_llc_occupancy_enabled())
> INIT_DELAYED_WORK(&d->cqm_limbo, cqm_handle_limbo);
>
> - /* If resctrl is mounted, add per domain monitor data directories. */
> - if (static_branch_unlikely(&rdt_mon_enable_key))
> + /*
> + * If the filesystem is not mounted then only the default resource group
> + * exists. Creation of its directories is deferred until mount time
> + * by rdt_get_tree() calling mkdir_mondata_all().
> + * If resctrl is mounted, add per domain monitor data directories.
> + */
> + if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
> mkdir_mondata_subdir_allrdtgrp(r, d);
>
> return 0;
--
Thanks
Babu Moger
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