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]
Date:   Wed, 27 Sep 2017 13:10:35 -0400
From:   Pasha Tatashin <pasha.tatashin@...cle.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        john.stultz@...aro.org, sboyd@...eaurora.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com, Peter Zijlstra <peterz@...radead.org>,
        Dou Liyang <douly.fnst@...fujitsu.com>
Subject: Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early
 in boot

Hi Russell,

This might be so for ARM, and in fact if you look at my SPARC 
implementation, I simply made source clock initialize early, so regular 
sched_clock() is used. As on SPARC, we use either %tick or %stick 
registers with frequency determined via OpenFrimware. But, on x86 there 
are dozen ways clock sources are setup, and some of them available quiet 
late in boot because of various dependencies. So, my early clock 
initialization for x86 (and expendable to other platforms with unstable 
clocks) is to make it available when TSC is available, which is 
determined by already existing kernel functionality in 
simple_udelay_calibration().

My goal was not to introduce any regressions to the already complex (in 
terms of number of branches and loads) sched_clock_cpu(), therefore I 
added a new function and avoided any extra branches through out the life 
of the system. I could mitigate some of that by using static branches, 
but imo the current approach is better.

Pasha

Powered by blists - more mailing lists