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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 29 Jun 2017 11:59:29 -0700
Message-ID: <CA+55aFz8Mhx+A-g-5yOG-O1ZLRUR_fpeeA4iBNGH8EnDBZEdpA@mail.gmail.com>
Subject: Re: [PATCH 2/4] swait: add the missing killable swaits
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Greg KH <gregkh@linuxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>, mfuzzey@parkeon.com,
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On Thu, Jun 29, 2017 at 11:33 AM, Davidlohr Bueso <dave@stgolabs.net> wrote:
> On Thu, 29 Jun 2017, Linus Torvalds wrote:
>
>> I actually think swait is pure garbage. Most users only wake up one
>> process anyway, and using swait for that is stupid. If you only wake
>> up one, you might as well just have a single process pointer, not a
>> wait list at all, and then use "wake_up_process()".
>
> But you still need the notion of a queue, even if you wake one task
> at a time... I'm probably missing your point here.

The *reason* they wake up only one seems to be that there really is
just one. It's some per-cpu idle thread for kvm, and for RCU it's the
RCU workqueue thread.

So the queue literally looks suspiciously pointless.

But I might be wrong, and there can actually be multiple entries. If
there are, I don't see why the wake-up-one semantics the code uses
would be valid, though.

                   Linus