linux-kernel - Re: [PATCH] buffer: Avoid setting buffer bits that are already set

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Date:   Mon, 23 Oct 2017 18:21:21 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     kemi <kemi.wang@...el.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Darrick J Wong <darrick.wong@...cle.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Dave <dave.hansen@...ux.intel.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Ying Huang <ying.huang@...el.com>,
        Aaron Lu <aaron.lu@...el.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] buffer: Avoid setting buffer bits that are already set

kemi <kemi.wang@...el.com> writes:
>
> I'll see if I can find some
>> time to implement the above in a nice way.
>
> Agree. Maybe something like test_and_set_bit() would be more suitable.

test_and_set_bit is a very different operation for the CPU because
it is atomic for both. But we want the initial read to not
be atomic.

If you add special functions use a different variant that is only
atomic for the set.

-Andi