From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Tejun Heo <tj@kernel.org>,
computersforpeace@gmail.com, Ingo Molnar <mingo@kernel.org>,
der.herr@hofr.at
Subject: Re: complete_all and "forever" completions
Date: Wed, 26 Oct 2016 10:45:35 +0200 [thread overview]
Message-ID: <20161026084535.GX3102@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20161025223054.GA22917@dtor-ws>
On Tue, Oct 25, 2016 at 03:30:54PM -0700, Dmitry Torokhov wrote:
> Hi,
>
> Reading Documentation/scheduler/completion.txt, complete_all() is
Oh, there is documentation? /me goes read.
> supposed to be usable with "forever" completions, i.e. when we have an
> action that happens once and stays "done" for the rest of lifetime of an
> object, no matter how many times we check for "doneness".
I suppose you allude to this wording:
"calls complete_all() to signal all current and future waiters."
> However the
> implementation for complete_all() simply sets the counter to be greater
> or equal UINT_MAX/2 and do_wait_for_common() happily decreases it on
> every call.
This is indeed so.
> Is it simply an artefact of [older] implementation where we do not
> expect to make that many calls to wait_for_completion*() so that
> completion that is signalled with ocmplete_all() is practically stays
> signalled forever?
The text says it was written against v3.18 or thereabout, and that
implementation looks a lot like todays, so I doubt it ever worked like
that.
> Or do we need something like this in
> do_wait_for_common():
>
> if (x->done < UINT_MAX/2)
> x->done--;
Depends a bit, do you really want this? Seems a bit daft to keep asking
if its done already, seems like a waste of cycles to me.
next prev parent reply other threads:[~2016-10-26 8:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-25 22:30 complete_all and "forever" completions Dmitry Torokhov
2016-10-26 8:45 ` Peter Zijlstra [this message]
2016-10-26 9:15 ` Nicholas Mc Guire
2016-10-27 9:51 ` Daniel Wagner
2016-10-26 12:10 ` Dmitry Torokhov
2016-10-26 15:42 ` Peter Zijlstra
2016-10-26 15:46 ` Peter Zijlstra
2016-10-26 17:12 ` Nicholas Mc Guire
2016-10-26 17:20 ` Dmitry Torokhov
2016-10-26 18:23 ` Dmitry Torokhov
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