From: Reinette Chatre <reinette.chatre@intel.com>
To: Ben Horgan <ben.horgan@arm.com>
Cc: <james.morse@arm.com>, <fenghuay@nvidia.com>,
<linux-kernel@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>, <tglx@linutronix.de>,
<mingo@redhat.com>, <bp@alien8.de>, <dave.hansen@linux.intel.com>,
<hpa@zytor.com>, <corbet@lwn.net>, <x86@kernel.org>,
<linux-doc@vger.kernel.org>, <dave.martin@arm.com>
Subject: Re: [PATCH v3 2/3] arm_mpam: resctrl: Add pass-through resctrl_arch_preconvert_bw()
Date: Fri, 5 Jun 2026 11:43:19 -0700 [thread overview]
Message-ID: <03e7cff2-bbfb-4c26-aa2c-a70127683a24@intel.com> (raw)
In-Reply-To: <20260515140612.1205251-3-ben.horgan@arm.com>
Hi Ben,
On 5/15/26 7:06 AM, Ben Horgan wrote:
> resctrl rounds up the percentage value of the MBA based on the bw_gran. As
> MPAM uses a binary fixed point fraction format for MBA rather than a
> decimal percentage, this introduces rounding errors.
>
> Without this additional rounding, if the user reads the value in an MB
> schema and then writes it back to the schema, the value in hardware won't
> change. However, with this additional rounding, this guarantee is broken
> for systems with mbw_wd < 7.
>
> resctrl is introducing resctrl_arch_preconvert_bw() to allow the arch code
> to specify the conversion resctrl does to the user-provided bandwidth
> value. Add the MPAM version of resctrl_arch_preconvert_bw(). This does no
> conversion.
>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
If rebased on patch #1 proposed changes:
| Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reinette
next prev parent reply other threads:[~2026-06-05 18:43 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-15 14:06 [PATCH v3 0/3] x86,fs/resctrl,arm_mpam: Factor MBA parse-time conversion to be per-arch Ben Horgan
2026-05-15 14:06 ` [PATCH v3 1/3] x86/resctrl: Add resctrl_arch_preconvert_bw() Ben Horgan
2026-06-05 18:42 ` Reinette Chatre
2026-05-15 14:06 ` [PATCH v3 2/3] arm_mpam: resctrl: Add pass-through resctrl_arch_preconvert_bw() Ben Horgan
2026-06-05 18:43 ` Reinette Chatre [this message]
2026-05-15 14:06 ` [PATCH v3 3/3] fs/resctrl: Factor MBA parse-time conversion to be per-arch Ben Horgan
2026-06-05 18:43 ` Reinette Chatre
2026-06-05 18:41 ` [PATCH v3 0/3] x86,fs/resctrl,arm_mpam: " Reinette Chatre
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