linux-kernel - Re: [RFC PATCH 7/7] lazy tlb: shoot lazies, a non-refcounting lazy tlb option

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Message-ID: <20200714132341.GY10769@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Jul 2020 15:23:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Anton Blanchard <anton@...abs.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        X86 ML <x86@...nel.org>
Subject: Re: [RFC PATCH 7/7] lazy tlb: shoot lazies, a non-refcounting lazy
 tlb option

On Tue, Jul 14, 2020 at 05:46:05AM -0700, Andy Lutomirski wrote:
> x86 has this exact problem. At least no more than 64*8 CPUs share the cache line :)

I've seen patches for a 'sparse' bitmap to solve related problems.

It's basically the same code, except it multiplies everything (size,
bit-nr) by a constant to reduce the number of active bits per line.

This sadly doesn't take topology into account, but reducing contention
is still good ofcourse.