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

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Message-ID: <20180831112029.GK24124@hirez.programming.kicks-ass.net>
Date:   Fri, 31 Aug 2018 13:20:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Nicholas Piggin <npiggin@...il.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 12:12:48PM +0100, Will Deacon wrote:
> On Fri, Aug 31, 2018 at 12:49:45PM +0200, Peter Zijlstra wrote:
> > 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..
> 
> You also can't IPI an IOMMU or a GPU ;)

Oh, right you are. I suppose that is why x86-iommu is using those mmu_notifiers.