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Date: Mon, 5 Oct 2020 11:35:06 +0200
From: Borislav Petkov <bp@...en8.de>
To: Fenghua Yu <fenghua.yu@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Stephane Eranian <eranian@...gle.com>,
Tony Luck <tony.luck@...el.com>,
Reinette Chatre <reinette.chatre@...el.com>,
Ravi V Shankar <ravi.v.shankar@...el.com>,
x86 <x86@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/resctrl: Correct MBM total and local values
On Mon, Sep 28, 2020 at 03:12:53PM -0700, Fenghua Yu wrote:
> MBM total and local readings are corrected by the following correction
> factor table on Broadwell server and Skylake server.
>
> core rmid rmid correction
> count count threshold factor
> 1 8 0 1.000000
> 2 16 0 1.000000
> 3 24 15 0.969650
> 4 32 0 1.000000
> 5 40 31 1.066667
> 6 48 31 0.969650
> 7 56 47 1.142857
> 8 64 0 1.000000
> 9 72 63 1.185115
> 10 80 63 1.066553
> 11 88 79 1.454545
> 12 96 0 1.000000
> 13 104 95 1.230769
> 14 112 95 1.142857
> 15 120 95 1.066667
> 16 128 0 1.000000
> 17 136 127 1.254863
> 18 144 127 1.185255
> 19 152 0 1.000000
> 20 160 127 1.066667
> 21 168 0 1.000000
> 22 176 159 1.454334
> 23 184 0 1.000000
> 24 192 127 0.969744
> 25 200 191 1.280246
> 26 208 191 1.230921
> 27 216 0 1.000000
> 28 224 191 1.143118
Table is already in the code, why is it needed in the commit message
too?
> If rmid > rmid threshold, MBM total and local values should be multipled
> by the correction factor.
>
> The above table is modified for better code:
> 1. The threshold 0 is changed to rmid count - 1 so we don't do correction
Who is "we"?
> for the case.
> 2. Correction factor is normalized to 2^20 for better performance
> by avoiding floating point and division calculation in corrected
> MBM values.
>
> Detailed information about the correction is described in erratum SKX99:
> https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html
> and BDF102: https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e5-v4-spec-update.pdf
>
> The problem is described in details in "3.6 Intel MBM RMID Imbalance":
> https://software.intel.com/content/www/us/en/develop/articles/intel-resource-director-technology-rdt-reference-manual.html
I hear those URLs are awfully unstable. I'd suggested you upload the
pdfs to bugzilla but the erratum text is short enough so that you can
simply add it here.
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
>
> Applied to tip:x86/cache.
>
> arch/x86/kernel/cpu/resctrl/core.c | 4 ++
> arch/x86/kernel/cpu/resctrl/internal.h | 1 +
> arch/x86/kernel/cpu/resctrl/monitor.c | 75 +++++++++++++++++++++++++-
> 3 files changed, 78 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 9e1712e8aef7..efe3ed61ae0c 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -893,6 +893,10 @@ static __init void __check_quirks_intel(void)
> set_rdt_options("!cmt,!mbmtotal,!mbmlocal,!l3cat");
> else
> set_rdt_options("!l3cat");
> + /* FALLTHROUGH */
WARNING: Prefer 'fallthrough;' over fallthrough comment
#89: FILE: arch/x86/kernel/cpu/resctrl/core.c:896:
+ /* FALLTHROUGH */
Have you heard of checkpatch.pl?
> + case INTEL_FAM6_BROADWELL_X:
> + intel_rdt_mbm_quirk();
> + break;
> }
...
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 54dffe574e67..05e06744e4b1 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -18,6 +18,7 @@
> #include <linux/module.h>
> #include <linux/slab.h>
> #include <asm/cpu_device_id.h>
> +#include <asm/intel-family.h>
> #include "internal.h"
>
> struct rmid_entry {
> @@ -64,6 +65,61 @@ unsigned int rdt_mon_features;
> */
> unsigned int resctrl_cqm_threshold;
>
> +#define CF(cf) ((unsigned long)(1048576 * (cf) + 0.5))
> +
> +/*
> + * MBM total and local correction table indexed by CBO which is equal to
"CBO" is?
> + * (x86_cache_max_rmid + 1) / 8 - 1 and is from 0 up to 27.
> + * The correction factor is normalized to 2^20 (1048576) so it's faster
> + * to calculate corrected value by shifting:
> + * corrected_value = (original_value * correction_factor) >> 20
> + */
> +static struct mbm_creation_factor_table {
> + u32 rmidthreshold;
> + u64 cf;
> +} mbm_cf_table[] = {
That array wants to be read-only right?
> + {7, CF(1.000000)},
> + {15, CF(1.000000)},
> + {15, CF(0.969650)},
> + {31, CF(1.000000)},
> + {31, CF(1.066667)},
> + {31, CF(0.969650)},
> + {47, CF(1.142857)},
> + {63, CF(1.000000)},
> + {63, CF(1.185115)},
> + {63, CF(1.066553)},
> + {79, CF(1.454545)},
> + {95, CF(1.000000)},
> + {95, CF(1.230769)},
> + {95, CF(1.142857)},
> + {95, CF(1.066667)},
> + {127, CF(1.000000)},
> + {127, CF(1.254863)},
> + {127, CF(1.185255)},
> + {151, CF(1.000000)},
> + {127, CF(1.066667)},
> + {167, CF(1.000000)},
> + {159, CF(1.454334)},
> + {183, CF(1.000000)},
> + {127, CF(0.969744)},
> + {191, CF(1.280246)},
> + {191, CF(1.230921)},
> + {215, CF(1.000000)},
> + {191, CF(1.143118)},
> +};
> +
> +static u32 mbm_cf_rmidthreshold = UINT_MAX;
> +static u64 mbm_cf;
> +
> +static inline u64 corrected_mbm_count(u32 rmid, unsigned long val)
Function name needs a verb.
> +{
> + /* Correct MBM value. */
> + if (rmid > mbm_cf_rmidthreshold)
> + val = (val * mbm_cf) >> 20;
> +
> + return val;
> +}
...
> @@ -644,3 +701,17 @@ int rdt_get_mon_l3_config(struct rdt_resource *r)
>
> return 0;
> }
> +
> +void intel_rdt_mbm_quirk(void)
Function name needs a verb.
> +{
> + int cf_index;
> +
> + cf_index = (boot_cpu_data.x86_cache_max_rmid + 1) / 8 - 1;
> + if (cf_index >= ARRAY_SIZE(mbm_cf_table)) {
> + pr_info("No MBM correction factor available\n");
> + return;
> + }
> +
> + mbm_cf_rmidthreshold = mbm_cf_table[cf_index].rmidthreshold;
> + mbm_cf = mbm_cf_table[cf_index].cf;
> +}
> --
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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