linux-kernel - Re: icache_is_aliasing and big.LITTLE

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Message-ID: <20190509085004.GE64514@C02TF0J2HF1T.local>
Date:   Thu, 9 May 2019 09:50:04 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Salman Qazi <sqazi@...gle.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: icache_is_aliasing and big.LITTLE

Hi,

On Wed, May 08, 2019 at 11:45:03AM -0700, Salman Qazi wrote:
> What is the intention behind icache_is_aliasing on big.LITTLE systems
> where some icaches are VIPT and others are PIPT? Is it meant to be
> conservative in some sense or should it be made per-CPU?

It needs to cover the worst case scenario across all CPUs, i.e. aliasing
VIPT if one of the CPUs has this. We can't make it per-CPU because a
thread performing cache maintenance might be migrated to another CPU
with different cache policy (e.g. sync_icache_aliases()).

-- 
Catalin