Messages in this thread | | | Date | Fri, 10 May 2019 12:04:18 +0100 | From | Mark Rutland <> | Subject | Re: icache_is_aliasing and big.LITTLE |
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On Thu, May 09, 2019 at 09:50:04AM +0100, Catalin Marinas wrote: > 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()).
It's slightly more subtle than that -- for broadcast maintenance the policy of the CPU receiving the broadcast matters.
So even if all i-cache maintenance were performed on a thread pinned to a CPU with PIPT caches, to correctly affect any VIPT i-caches in the system it would be necessary to perform maintenance as-if the CPU performing the maintenance had VIPT i-caches.
Thanks, Mark.
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