linux-kernel - Re: [PATCH v1 12/20] x86/recstrl: Add per-rmid arch private storage for overflow and chunks

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Date:   Wed, 11 Aug 2021 18:14:11 +0100
From:   Jamie Iles <jamie@...iainc.com>
To:     James Morse <james.morse@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        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>,
        Babu Moger <Babu.Moger@....com>,
        shameerali.kolothum.thodi@...wei.com,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        lcherian@...vell.com, bobo.shaobowang@...wei.com
Subject: Re: [PATCH v1 12/20] x86/recstrl: Add per-rmid arch private storage
 for overflow and chunks

Hi James,

On Thu, Jul 29, 2021 at 10:36:02PM +0000, James Morse wrote:
> resctrl_arch_rmid_read() is intended as the function that an
> architecture agnostic resctrl filesystem driver can use to
> read a value in bytes from a counter. Currently the function returns
> the mbm values in chunks directly from hardware. For bandwidth
> counters the resctrl filesystem provides the number of bytes
> ever seen. Internally mba_sc uses a second prev_bw_msr to calculate
> the bytes read since the last mba_sc invocation.
> 
> MPAM's scaling of counters can be changed at runtime, reducing the
> resolution but increasing the range. When this is changed the prev_msr
> values need to be converted by the architecture code.
> 
> Add storage for per-rmid private storage. The prev_msr and chunks
> values will move here to allow resctrl_arch_rmid_read() to always
> return the number of bytes read by this counter.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
>  arch/x86/kernel/cpu/resctrl/core.c     | 29 ++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/resctrl/internal.h | 13 ++++++++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 8a3c13c6c19f..27c93d12ca27 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -432,6 +432,28 @@ static int domain_setup_ctrlval(struct rdt_resource *r, struct rdt_domain *d)
>  	return 0;
>  }
>  
> +static int arch_domain_mbm_alloc(u32 num_rmid, struct rdt_hw_domain *hw_dom)
> +{
> +	size_t tsize;
> +
> +	if (is_mbm_total_enabled()) {
> +		tsize = sizeof(*hw_dom->arch_mbm_total);
> +		hw_dom->arch_mbm_total = kcalloc(num_rmid, tsize, GFP_KERNEL);
> +		if (!hw_dom->arch_mbm_total)
> +			return -ENOMEM;
> +	}
> +	if (is_mbm_local_enabled()) {
> +		tsize = sizeof(*hw_dom->arch_mbm_local);
> +		hw_dom->arch_mbm_local = kcalloc(num_rmid, tsize, GFP_KERNEL);
> +		if (!hw_dom->arch_mbm_local) {
> +			kfree(hw_dom->arch_mbm_total);
> +			return -ENOMEM;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * domain_add_cpu - Add a cpu to a resource's domain list.
>   *
> @@ -481,6 +503,11 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
>  		return;
>  	}
>  
> +	if (r->mon_capable && arch_domain_mbm_alloc(r->num_rmid, hw_dom)) {
> +		kfree(d);

Does this error path and subsequent ones in domain_add_cpu also need to 
undo the allocations from arch_domain_mbm_alloc?

Thanks,

Jamie