linux-kernel - Re: [RFC 3/3] sched: depend on 64BIT_ATOMIC_ACCESS to determine if to use min_vruntime

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Date:   Thu, 24 Aug 2017 10:49:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hoeun Ryu <hoeun.ryu@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Ingo Molnar <mingo@...nel.org>, Michal Marek <mmarek@...e.com>,
        Laura Abbott <labbott@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>, mic@...ikod.net,
        Russell King <linux@...linux.org.uk>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Jonathan Austin <jonathan.austin@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC 3/3] sched: depend on 64BIT_ATOMIC_ACCESS to determine if
 to use min_vruntime_copy

On Thu, Aug 24, 2017 at 02:42:57PM +0900, Hoeun Ryu wrote:
> +#ifndef CONFIG_64BIT_ATOMIC_ALIGNED_ACCESS
>  	u64 min_vruntime;
> -#ifndef CONFIG_64BIT
> +#else
> +	u64 min_vruntime __attribute__((aligned(sizeof(u64))));
> +#endif

That's stupid, just make sure your platform defines u64 as naturally
aligned when you have this 64BIT_ATOMIC foo.

Also, please try and dig out more 32bit archs that can use this and make
sure to include performance numbers to justify this extra cruft.