linux-kernel - Re: [PATCH 00/12] Avoid synchronous TLB invalidation for intermediate page-table entries on arm64

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Message-ID: <20180831104945.GI24124@hirez.programming.kicks-ass.net>
Date:   Fri, 31 Aug 2018 12:49:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Will Deacon <will.deacon@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@....ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 00/12] Avoid synchronous TLB invalidation for
 intermediate page-table entries on arm64

On Fri, Aug 31, 2018 at 08:32:34PM +1000, Nicholas Piggin wrote:
> Oh gee, I suppose. powerpc hash is kind of interesting because it's
> crazy, Aneesh knows that code a lot better than I do. radix modulo
> some minor details of exact instructions is fairly like x86 

The whole TLB broadcast vs explicit IPIs is a fairly big difference in
my book.

Anyway, have you guys tried the explicit IPI approach? Depending on how
IPIs are routed vs broadcasts it might save a little bus traffic. No
point in getting all CPUs to process the TLBI when there's only a hand
full that really need it.

OTOH, I suppose the broadcast thing has been optimized to death on the
hardware side, so who knows..