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Date: Mon, 14 Aug 2023 19:59:33 -0700
From: Fenghua Yu <fenghua.yu@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
<linux-kernel@...r.kernel.org>
CC: 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>,
Babu Moger <Babu.Moger@....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>,
<xingxin.hx@...nanolis.org>, <baolin.wang@...ux.alibaba.com>,
Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, <peternewman@...gle.com>,
<dfustini@...libre.com>
Subject: Re: [PATCH v5 08/24] x86/resctrl: Allocate the cleanest CLOSID by
searching closid_num_dirty_rmid
Hi, James,
On 7/28/23 09:42, James Morse wrote:
> MPAM's PMG bits extend its PARTID space, meaning the same PMG value can be
> used for different control groups.
>
> This means once a CLOSID is allocated, all its monitoring ids may still be
> dirty, and held in limbo.
>
> Instead of allocating the first free CLOSID, on architectures where
> CONFIG_RESCTRL_RMID_DEPENDS_ON_COSID is enabled, search
> closid_num_dirty_rmid[] to find the cleanest CLOSID.
>
> The CLOSID found is returned to closid_alloc() for the free list
> to be updated.
>
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v4:
> * Dropped stale section from comment
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 2 ++
> arch/x86/kernel/cpu/resctrl/monitor.c | 42 ++++++++++++++++++++++++++
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++---
> 3 files changed, 58 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 94749ee950dd..7c2a1c235480 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -557,5 +557,7 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
> void __init thread_throttle_mode_init(void);
> void __init mbm_config_rftype_init(const char *config);
> void rdt_staged_configs_clear(void);
> +bool closid_allocated(unsigned int closid);
> +int resctrl_find_cleanest_closid(void);
>
> #endif /* _ASM_X86_RESCTRL_INTERNAL_H */
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 44addc0126fc..c268aa5925c7 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -379,6 +379,48 @@ static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
> return ERR_PTR(-ENOSPC);
> }
>
> +/**
> + * resctrl_find_cleanest_closid() - Find a CLOSID where all the associated
> + * RMID are clean, or the CLOSID that has
> + * the most clean RMID.
> + *
> + * MPAM's equivalent of RMID are per-CLOSID, meaning a freshly allocated CLOSID
> + * may not be able to allocate clean RMID. To avoid this the allocator will
> + * choose the CLOSID with the most clean RMID.
> + *
> + * When the CLOSID and RMID are independent numbers, the first free CLOSID will
> + * be returned.
> + */
> +int resctrl_find_cleanest_closid(void)
> +{
> + u32 cleanest_closid = ~0, iter_num_dirty;
> + int i = 0;
> +
> + lockdep_assert_held(&rdtgroup_mutex);
> +
> + if (!IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID))
> + return -EIO;
> +
> + for (i = 0; i < closids_supported(); i++) {
> + if (closid_allocated(i))
> + continue;
> +
> + iter_num_dirty = closid_num_dirty_rmid[i];
> + if (iter_num_dirty == 0)
> + return i;
> +
> + if (cleanest_closid == ~0)
> + cleanest_closid = i;
> +
> + if (iter_num_dirty < closid_num_dirty_rmid[cleanest_closid])
> + cleanest_closid = i;
> + }
> +
> + if (cleanest_closid == ~0)
> + return -ENOSPC;
> + return cleanest_closid;
> +}
> +
resctrl_find_cleanest_closid() is not empty on x86 after compiled
although it's very short. After all, the function is irrelevant to x86
and could be completely empty on x86.
If put the function in
#ifdef CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID
resctrl_find_cleanest_closid()
...
#else
resctrl_find_cleanest_closid() {}
#endif
It's fully empty on x86.
> /*
> * For MPAM the RMID value is not unique, and has to be considered with
> * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 4ab9bb018c17..df28b81d2c9c 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -132,11 +132,20 @@ static void closid_init(void)
>
> static int closid_alloc(void)
> {
> - u32 closid = ffs(closid_free_map);
> + u32 closid;
> + int err;
>
> - if (closid == 0)
> - return -ENOSPC;
> - closid--;
> + if (IS_ENABLED(CONFIG_RESCTRL_RMID_DEPENDS_ON_CLOSID)) {
> + err = resctrl_find_cleanest_closid();
> + if (err < 0)
> + return err;
> + closid = err;
> + } else {
> + closid = ffs(closid_free_map);
> + if (closid == 0)
> + return -ENOSPC;
> + closid--;
> + }
> clear_bit(closid, &closid_free_map);
>
> return closid;
> @@ -154,7 +163,7 @@ void closid_free(int closid)
> * Return: true if @closid is currently associated with a resource group,
> * false if @closid is free
> */
> -static bool closid_allocated(unsigned int closid)
> +bool closid_allocated(unsigned int closid)
> {
> return !test_bit(closid, &closid_free_map);
> }
Thanks.
-Fenghua
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