linux-kernel - Re: [PATCH v14 25/25] sched: use static key for sched_clock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGM2reZYcKqoSBZQmUP-CMO=2bLznahLjzp=t0xiTxGsAMsEng@mail.gmail.com>
Date:   Thu, 19 Jul 2018 10:24:40 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     peterz@...radead.org
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        John Stultz <john.stultz@...aro.org>, sboyd@...eaurora.org,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com, prarit@...hat.com, feng.tang@...el.com,
        Petr Mladek <pmladek@...e.com>, gnomes@...rguk.ukuu.org.uk,
        linux-s390@...r.kernel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, pbonzini@...hat.com
Subject: Re: [PATCH v14 25/25] sched: use static key for sched_clock_running

On Thu, Jul 19, 2018 at 6:49 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jul 17, 2018 at 10:22:11PM -0400, Pavel Tatashin wrote:
> > sched_clock_running may be read every time sched_clock_cpu() is called.
> > Yet, this variable is updated only twice during boot, and never changes
> > again, therefore it is better to make it a static key.
>
> Right, so the focus was always on making the sane TSC case fast, and if
> TSC isn't stable we'd just make do and not care too much.
>

True for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, but for other systems like
SPARC, it hurts to have this variable accessed every time, even though
they have a sane sched_clock().

> But this certainly isn't wrong, so ACK.

Thank you,
Pave