linux-kernel - Re: [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush instruction within the same inner shareable domain

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Message-ID: <675313fe-007b-c850-d730-a629b82ccfc8@jonmasters.org>
Date:   Mon, 8 Jul 2019 20:25:52 -0400
From:   Jon Masters <jcm@...masters.org>
To:     "qi.fuli@...itsu.com" <qi.fuli@...itsu.com>,
        Will Deacon <will@...nel.org>
Cc:     Will Deacon <will.deacon@....com>,
        "indou.takao@...itsu.com" <indou.takao@...itsu.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jonathan Corbet <corbet@....net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/2] arm64: Introduce boot parameter to disable TLB flush
 instruction within the same inner shareable domain

On 7/2/19 10:45 PM, qi.fuli@...itsu.com wrote:

> However, we found that with the increase of that the TLB flash was called,
> the noise was also increasing. Here we understood that the cause of this 
> issue is the implementation of Linux's TLB flush for arm64, especially use of 
> TLBI-is instruction which is a broadcast to all processor core on the system. 

Are you saying that for a microbenchmark in which very large numbers of
threads are created and destroyed rapidly there are a large number of
associated tlb range flushes which always use broadcast TLBIs?

If that's the case, and the hardware doesn't do any ASID filtering and
each TLBI results in a DVM to every PE, would it make sense to look at
whether there are ways to improve batching/switch to an IPI approach
rather than relying on broadcasts, as a more generic solution?

Jon.