RE: [PATCH V3 3/4] x86/resctrl: Enable per-thread MBA

Babu Moger
2020-05-14T19:04:42Z

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@intel.com>
> Sent: Wednesday, May 6, 2020 6:50 PM
> To: tglx@linutronix.de; fenghua.yu@intel.com; bp@alien8.de;
> tony.luck@intel.com
> Cc: kuo-lang.tseng@intel.com; ravi.v.shankar@intel.com; mingo@redhat.com;
> Moger, Babu <Babu.Moger@amd.com>; hpa@zytor.com; x86@kernel.org;
> linux-kernel@vger.kernel.org; Reinette Chatre <reinette.chatre@intel.com>
> Subject: [PATCH V3 3/4] x86/resctrl: Enable per-thread MBA
>
> From: Fenghua Yu <fenghua.yu@intel.com>
>
> Current Memory Bandwidth Allocation (MBA) hardware has a limitation:
> all threads on the same core must have the same delay value. If there
> are different delay values across threads on one core, the original
> MBA implementation allocates the max delay value to the core and an
> updated implementation allocates either min or max delay value specified
> by a configuration MSR across threads on the core.
>
> Newer systems support per-thread MBA such that each thread is allocated
> with its own delay value.
>
> If per-thread MBA is supported, report "per-thread" in resctrl file
> "info/MB/thread_throttle_mode" to let user applications know memory
> bandwidth is allocated per thread and help them fine tune MBA on thread
> level.
>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Changes since V2:
> - Fix rST formatting of documentation (resctrl_ui.rst) describing
> new "thread_throttle_mode" resctrl file.
> - Use boot_cpu_has() instead of static_cpu_has() when determining what
> to display to user (slow path).
>
> Documentation/x86/resctrl_ui.rst | 3 +++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 11 +++++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/Documentation/x86/resctrl_ui.rst
> b/Documentation/x86/resctrl_ui.rst
> index 861ee2816470..1b066d1aafad 100644
> --- a/Documentation/x86/resctrl_ui.rst
> +++ b/Documentation/x86/resctrl_ui.rst
> @@ -150,6 +150,9 @@ with respect to allocation:
> "max":
> the smallest percentage is applied
> to all threads
> + "per-thread":
> + bandwidth percentages are directly applied to
> + the threads running on the core
>
> If RDT monitoring is available there will be an "L3_MON" directory
> with the following files:
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 6a9408060ac4..c60a3b307f7d 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1038,12 +1038,23 @@ static int max_threshold_occ_show(struct
> kernfs_open_file *of,
> * with the maximum delay value that from the software interface will be
> * the minimum of the bandwidth percentages assigned to the hardware threads
> * sharing the core.
> + *
> + * Some systems (identified by X86_FEATURE_PER_THREAD_MBA enumerated
> via CPUID)
> + * support per-thread MBA. On these systems hardware doesn't apply the
> minimum
> + * or maximum delay value to all threads in a core. Instead, a thread is
> + * allocated with the delay value that is assigned to the thread.
> */
> static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
> struct seq_file *seq, void *v)
> {
> unsigned int throttle_mode = 0;
>
> + if (boot_cpu_has(X86_FEATURE_PER_THREAD_MBA)) {
> + seq_puts(seq, "per-thread\n");
> +
You probably don't need an extra line here.

> + return 0;
> + }
> +
> if (mba_cfg_supports_min_max_intel())
> throttle_mode = mba_cfg_msr &
> MBA_THROTTLE_MODE_MASK;
>
> --
> 2.21.0