Date: Wed, 28 Jun 2017 12:03:11 -0700
From: Davidlohr Bueso <dave@stgolabs.net>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>, DanielWagnerwagi@monom.org,
        Boqun Feng <boqun.feng@gmail.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Ming Lei <ming.lei@redhat.com>, "Li, Yi" <yi1.li@linux.intel.com>,
        "AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Petr Mladek <pmladek@suse.com>, Andrew Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>, David Howells <dhowells@redhat.com>,
        Alan Cox <alan@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>,
        oss-drivers@netronome.com
Subject: Re: [PATCH] firmware: wake all waiters
Message-ID: <20170628190311.GA27814@linux-80c1.suse>
References: <20170623233702.20564-1-jakub.kicinski@netronome.com>
 <CA+55aFxivLtaFEur99eZpoafcweK1WNvSu2vEvxXvj5gKB8CdA@mail.gmail.com>
 <20170626233030.GI21846@wotan.suse.de>
 <CA+55aFzjrGsFvt56YPo-1tN7ZEPPANaO5ZVNxUS18JAiHdz83g@mail.gmail.com>
 <20170627001534.GK21846@wotan.suse.de>
 <20170628134514.GA2644@linux-80c1.suse>
 <20170628155851.GF21846@wotan.suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <20170628155851.GF21846@wotan.suse.de>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1436
Lines: 37

Hi Luis!

On Wed, 28 Jun 2017, Luis R. Rodriguez wrote:

>On Wed, Jun 28, 2017 at 06:45:14AM -0700, Davidlohr Bueso wrote:
>> On Tue, 27 Jun 2017, Luis R. Rodriguez wrote:
>>
>> > diff --git a/include/linux/swait.h b/include/linux/swait.h
>> > index 4a4e180d0a35..14fcf23cece4 100644
>> > --- a/include/linux/swait.h
>> > +++ b/include/linux/swait.h
>> > @@ -29,7 +29,10 @@
>> >  *
>> >  * As a side effect of this; the data structures are slimmer.
>> >  *
>> > - * One would recommend using this wait queue where possible.
>>
>> So I think this was added due to the smaller footprint and fewer
>> cycles that swait has compared to the traditional (bulkier)
>> waitqueues. While probably not worth it, I guess we could offer
>> super-simple waitqueues (sswait? :-) which do not have the rt caveats
>> and uses a regular spinlock. The wakeup_all() call would not drop
>> the lock upon every wakeup as we are stripping the waitqueue not
>> for determinism, but for overhead. To mitigate this, we might
>> also want to use wake_q for reduced hold q->lock hold times.
>>
>> But I don't think its worth yet another wait interface.
>> Alternatively, it crossed my mind we could also have wakeup_all()
>> use in the regular waitqueues, but I'd have to audit all the
>> current users to make sure we could actually do this.
>
>But this open-welcoming invite for swait then, should it go?

I have nothing against removing it.

Thanks,
Davidlohr