linux-kernel - RE: About add an A64FX cache control function into resctrl

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Message-ID: <TYAPR01MB63306067FB5BF24BE15B3E3A8B2D9@TYAPR01MB6330.jpnprd01.prod.outlook.com>
Date:   Mon, 17 May 2021 08:29:38 +0000
From:   "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>
To:     'Catalin Marinas' <catalin.marinas@....com>,
        "Luck, Tony" <tony.luck@...el.com>
CC:     "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'linux-arm-kernel@...ts.infradead.org'" 
        <linux-arm-kernel@...ts.infradead.org>,
        'James Morse' <james.morse@....com>,
        "misono.tomohiro@...itsu.com" <misono.tomohiro@...itsu.com>
Subject: RE: About add an A64FX cache control function into resctrl

Hi, Tony, Catalin

> On Thu, Apr 29, 2021 at 05:50:20PM +0000, Luck, Tony wrote:
> > >>>> [Sector cache function]
> > >>>> The sector cache function split cache into multiple sectors and
> > >>>> control them separately. It is implemented on the L1D cache and
> > >>>> L2 cache in the A64FX processor and can be controlled
> > >>>> individually for L1D cache and L2 cache. A64FX has no L3 cache.
> > >>>> Each L1D cache and
> > >>>> L2 cache has 4 sectors. Which L1D sector is used is specified by
> > >>>> the value of [57:56] bits of address, how many ways of sector are
> > >>>> specified by the value of register (IMP_SCCR_L1_EL0).
> > >>>> Which L2 sector is used is specified by the value of [56] bits of
> > >>>> address, and how many ways of sector are specified by value of
> > >>>> register (IMP_SCCR_ASSIGN_EL1, IMP_SCCR_SET0_L2_EL1,
> > >>>> IMP_SCCR_SET1_L2_EL1).
> >
> > Are A64FX binaries position independent?  I.e. could the OS reassign a
> > running task to a different sector by remapping it to different
> > virtual addresses during a context switch?
> 
> Arm64 supports a maximum of 52-bit of virtual or physical addresses. The
> maximum the MMU would produce would be a 52-bit output address. I
> presume bits 56, 57 of the address bus are used for some cache affinity (sector
> selection) but they don't influence the memory addressing, nor could the MMU
> set them.
Yes, A64FX binaries are position independent. Arm64 supports 
a maximum of 52-bit of virtual or physical address. On A64FX, 
the [56:57] bits of virtual addresses are used for some cache 
affinity (sector selection) and set by user program instead of MMU.

Best regards,
Tan Shaopeng