Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 18 Nov 2019 08:41:37 -0600
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Shile Zhang' <shile.zhang@linux.alibaba.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "x86@kernel.org" <x86@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>
Subject: Re: [RFC PATCH v3 7/7] x86/unwind/orc: remove run-time ORC unwind
 tables sort
Message-ID: <20191118144137.ibxel2hmp57jvspc@treble>
References: <20191115064750.47888-1-shile.zhang@linux.alibaba.com>
 <20191115064750.47888-8-shile.zhang@linux.alibaba.com>
 <893d3caf85cd4ed0921fab84cfe28cad@AcuMS.aculab.com>
 <20191115174649.ldif5o7xqo5ntxeo@treble>
 <5fe9024bc69c4a4eb115b3c2f3f9bcd1@AcuMS.aculab.com>
MIME-Version: 1.0
In-Reply-To: <5fe9024bc69c4a4eb115b3c2f3f9bcd1@AcuMS.aculab.com>
User-Agent: NeoMutt/20180716
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Nov 18, 2019 at 10:05:02AM +0000, David Laight wrote:
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> > Sent: 15 November 2019 17:47
> > On Fri, Nov 15, 2019 at 04:51:24PM +0000, David Laight wrote:
> > > From: Shile Zhang
> > > > Sent: 15 November 2019 06:48
> > > ...
> > > >  arch/x86/kernel/unwind_orc.c | 8 +++++---
> > > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_=
orc.c
> > > > index 332ae6530fa8..280da6fa9922 100644
> > > > --- a/arch/x86/kernel/unwind_orc.c
> > > > +++ b/arch/x86/kernel/unwind_orc.c
> > > > @@ -273,9 +273,11 @@ void __init unwind_init(void)
> > > >  =09=09return;
> > > >  =09}
> > > >
> > > > -=09/* Sort the .orc_unwind and .orc_unwind_ip tables: */
> > > > -=09sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_=
cmp,
> > > > -=09     orc_sort_swap);
> > > > +=09/*
> > > > +=09 * Note, orc_unwind and orc_unwind_ip tables has been sorted in
> > > > +=09 * vmlinux link phase by sorttable tool at build time.
> > > > +=09 * Its ready for binary search now.
> > > > +=09 */
> > >
> > > How fast is sort() if the table is sorted?
> > > Relying on the kernel sources and build scripts always being in sync =
seems dangerous.
> > > Probably better to leave the sort in for a release of two.
> >=20
> > This patch comes after the build script changes, so they'd be in sync.
> > What would the concern be?
>=20
> Mostly that if, for any reason, the build script changes are missing noth=
ing
> will detect the error - but the results will be very confusing.
> If the sort is fast for sorted inputs (some algorithms aren't) then leavi=
ng
> it in won't take that long.

But why would the build script changes be missing...

And it should fail gracefully for oopses anyway: stack traces will just
have a bunch of question marks.

--=20
Josh