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Date: Mon, 13 Apr 2015 21:17:50 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: rusty@rustcorp.com.au, mathieu.desnoyers@efficios.com, oleg@redhat.com,
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        Andrea Arcangeli <aarcange@redhat.com>,
        David Woodhouse <David.Woodhouse@intel.com>,
        Rik van Riel <riel@redhat.com>, Michel Lespinasse <walken@google.com>
Subject: Re: [PATCH v5 05/10] seqlock: Better document
 raw_write_seqcount_latch()
Message-ID: <20150413191750.GK23123@twins.programming.kicks-ass.net>
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 <20150413141213.492831596@infradead.org>
 <20150413163201.GC6040@gmail.com>
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On Mon, Apr 13, 2015 at 06:32:02PM +0200, Ingo Molnar wrote:
> 
> Btw., I realize this is just a sample, but couldn't this be written 
> more optimally as:
> 
> 	do {
> 		seq = READ_ONCE(latch->seq);
> 		smp_read_barrier_depends();
> 
> 		idx = seq & 0x01;
> 		entry = data_query(latch->data[idx], ...);
> 
> 		smp_rmb();
> 	} while (seq != latch->seq);
> 

So in the actual code we use raw_read_seqcount() which includes the rmb.

This is true for the existing __ktime_get_fast_ns() as we as the new
latch_tee_find().

Should we look at introducing yet another seq primitive?