linux-kernel - Re: [RFC][PATCH] sched/wait_bit: Introduce wait_var_event()/wake_up

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Date:   Thu, 15 Mar 2018 15:53:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Ingo Molnar <mingo@...hat.com>, Christoph Hellwig <hch@....de>,
        david <david@...morbit.com>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jan Kara <jack@...e.cz>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [RFC][PATCH] sched/wait_bit: Introduce
 wait_var_event()/wake_up_var()

On Thu, Mar 15, 2018 at 02:45:20PM +0000, David Howells wrote:
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Does the below address things sufficiently clear?
> 
> Yep.

Thanks!

> > +wait_queue_head_t *__var_waitqueue(void *p)
> > +{
> > +	if (BITS_PER_LONG == 64) {
> > +		unsigned long q = (unsigned long)p;
> > +
> > +		return bit_waitqueue((void *)(q & ~1), q & 1);
> > +	}
> > +	return bit_waitqueue(p, 0);
> > +}
> 
> You might be better off not using bit_waitqueue() but rather do the
> calculation directly since you don't actually have a bit number.

Yes, I did that in patch 11. The initial version uses the exact same
stuff wait_on_atomic_t() uses to avoid spurious changes.