From: Marcelo Tosatti <mtosatti@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>, h@amt.cnet
Cc: Thomas Gleixner <tglx@linutronix.de>,
Greg KH <gregkh@linuxfoundation.org>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
mfuzzey@parkeon.com, "Eric W. Biederman" <ebiederm@xmission.com>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Daniel Wagner <wagi@monom.org>,
David Woodhouse <dwmw2@infradead.org>,
jewalt@lgsinnovations.com, rafal@milecki.pl,
Arend Van Spriel <arend.vanspriel@broadcom.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
"Li, Yi" <yi1.li@linux.intel.com>,
atull@kernel.org, Moritz Fischer <moritz.fischer@ettus.com>,
Petr Mladek <pmladek@suse.com>,
Johannes Berg <johannes.berg@intel.com>,
Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
"Coelho, Luciano" <luciano.coelho@intel.com>,
Kalle Valo <kvalo@codeaurora.org>,
Andrew Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
"AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
David Howells <dhowells@redhat.com>,
Peter Jones <pjones@redhat.com>,
Hans de Goede <hdegoede@redhat.com>,
Alan Cox <alan@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Matthew Wilcox <mawilcox@microsoft.com>,
Linux API <linux-api@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"stable # 4 . 6" <stable@vger.kernel.org>
Subject: Re: [PATCH 2/4] swait: add the missing killable swaits
Date: Thu, 29 Jun 2017 16:15:07 -0300 [thread overview]
Message-ID: <20170629191506.GB12368@amt.cnet> (raw)
In-Reply-To: <CA+55aFxkp51RipBj7__T0hoy6tAdXJxTqjMdhnnnkKm71P6HuQ@mail.gmail.com>
On Thu, Jun 29, 2017 at 09:13:29AM -0700, Linus Torvalds wrote:
> On Thu, Jun 29, 2017 at 6:46 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Thu, 29 Jun 2017, Greg KH wrote:
> >> On Thu, Jun 29, 2017 at 03:05:26PM +0200, Thomas Gleixner wrote:
> >> >
> >> > And who defined that it should not be used in real code?
> >>
> >> Linus did, in a different firmware thread. You have to _really_ know
> >> what you are doing to use this interface, and the firmware interface
> >> shouldn't be using it. So adding new apis just for firmware does not
> >> seem like a wise decision at this point in time.
> >
> > So it's not about code in general, it's about a particular piece of
> > code. Fair enough.
>
> Well, I'd actually say it the other way around: swait should not be
> used in general, only in _very_ particular pieces of code that
> actually explicitly need the odd swait semantics.
>
> swait uses special locking and has odd semantics that are not at all
> the same as the default wait queue ones. It should not be used without
> very strong reasons (and honestly, the only strong enough reason seems
> to be "RT").
Performance shortcut:
https://lkml.org/lkml/2016/2/25/301
> The special locking means that swait doesn't do DEBUG_LOCK_ALLOC, but
> it also means that it doesn't even work in all contexts.
>
> So "swake_up()" does surprising things (only wake up one - that's what
> caused a firmware loading bug), and "swake_up_all()" has magic rules
> about interrupt disabling.
>
> The thing is simply a collection of small hacks and should NOT be used
> in general.
Its a very smart performance speed up ;-)
> I never want to see a driver use that code, for example. It was
> designed for RCU and RT, and it should damn well be limited to that.
>
> Linus
If KVM is the only user, feel free to remove it, you're past the point
where that performance improvement matters (due to VMX hardware
improvements).
next prev parent reply other threads:[~2017-06-30 2:37 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-14 22:20 [PATCH 0/4] firmware: fix fallback mechanism by ignoring SIGCHLD Luis R. Rodriguez
2017-06-14 22:20 ` [PATCH 1/4] test_firmware: add test case for SIGCHLD on sync fallback Luis R. Rodriguez
2017-06-14 22:20 ` [PATCH 2/4] swait: add the missing killable swaits Luis R. Rodriguez
2017-06-29 12:54 ` Greg KH
2017-06-29 13:05 ` Thomas Gleixner
2017-06-29 13:35 ` Greg KH
2017-06-29 13:46 ` Thomas Gleixner
2017-06-29 16:13 ` Linus Torvalds
2017-06-29 16:31 ` Matthew Wilcox
2017-06-29 17:29 ` Luis R. Rodriguez
2017-06-29 17:40 ` Davidlohr Bueso
2017-06-29 17:57 ` Linus Torvalds
2017-06-29 18:33 ` Davidlohr Bueso
2017-06-29 18:59 ` Linus Torvalds
2017-06-29 19:40 ` Luis R. Rodriguez
2017-06-29 19:44 ` Luis R. Rodriguez
2017-06-29 20:58 ` Jakub Kicinski
2017-06-29 22:50 ` Luis R. Rodriguez
2017-06-29 22:53 ` Jakub Kicinski
2017-06-29 23:00 ` Luis R. Rodriguez
2017-06-29 23:06 ` Jakub Kicinski
2017-07-12 21:33 ` Luis R. Rodriguez
2017-06-29 20:57 ` Linus Torvalds
2017-07-05 2:06 ` Davidlohr Bueso
2017-07-07 19:58 ` Linus Torvalds
2017-07-07 22:27 ` Davidlohr Bueso
2017-07-07 22:48 ` Linus Torvalds
2017-06-29 19:15 ` Marcelo Tosatti [this message]
2017-06-30 4:03 ` Linus Torvalds
2017-06-30 11:55 ` Marcelo Tosatti
2017-06-30 11:57 ` Marcelo Tosatti
2017-06-30 17:30 ` Krister Johansen
2017-06-14 22:20 ` [PATCH 3/4] firmware: avoid invalid fallback aborts by using killable swait Luis R. Rodriguez
2017-06-14 22:20 ` [PATCH 4/4] firmware: send -EINTR on signal abort on fallback mechanism Luis R. Rodriguez
2017-06-15 7:49 ` [PATCH 0/4] firmware: fix fallback mechanism by ignoring SIGCHLD Martin Fuzzey
2017-06-26 21:19 ` Luis R. Rodriguez
2017-06-29 15:14 ` Greg KH
2017-06-29 17:29 ` Luis R. Rodriguez
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