linux-kernel - Re: [PATCH 6/8] lazy tlb: shoot lazies, a non-refcounting lazy tlb option

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Message-ID: <20201130093417.GI3092@hirez.programming.kicks-ass.net>
Date:   Mon, 30 Nov 2020 10:34:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux-MM <linux-mm@...ck.org>, Anton Blanchard <anton@...abs.org>
Subject: Re: [PATCH 6/8] lazy tlb: shoot lazies, a non-refcounting lazy tlb
 option

On Mon, Nov 30, 2020 at 10:30:00AM +0100, Peter Zijlstra wrote:
> On Sat, Nov 28, 2020 at 07:54:57PM -0800, Andy Lutomirski wrote:
> > This means that mm_cpumask operations won't need to be full barriers
> > forever, and we might not want to take the implied full barriers in
> > set_bit() and clear_bit() for granted.
> 
> There is no implied full barrier for those ops.

Neither ARM nor Power implies any ordering on those ops. But Power has
some of the worst atomic performance in the world despite of that.

IIRC they don't do their LL/SC in L1.