Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1271007

Re: [RFC PATCH -v2.1] x86: Kill notsc

Show all headers | View raw

On Tue, Nov 17, 2015 at 10:11:03AM +0100, Thomas Gleixner wrote:
> There is an interesting problem:
> 
> tsc_init()
> {
>        tsc_khz = x86_platform.calibrate_tsc();
>        if (!tsc_khz) {
>        	  mark_tsc_unstable("could not calculate TSC khz");
> 	  ...
>        }
> 
> In the current code we do NOT use TSC for sched_clock() and that's
> correct as we have no idea what the TSC frequency is.
> 
> With your changes that is not longer the case, so you end up with a
> completely wreckaged sched clock.

Hmm, I see it.

Well, I had a related splat which bombed because cyc2ns_init() had to
run before we do sched_init()->idle_init() which called sched_clock()
and there we did the cycles_2_ns() thing and the percpu vars weren't
initialized yet.

That's why I did this:

+void __init early_tsc_init(void)
+{
+       int cpu;
+
+       /*
+        * We need to init the cycles to ns conversion machinery because
+        * init_idle() below will call sched_clock() which needs it.
+        */
+       for_each_possible_cpu(cpu)
+               cyc2ns_init(cpu);
+}

Maybe I should move tsc_init() before sched_init() so that the
calibration happens before we use the TSC in sched_clock() for the first
time...?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[RFC PATCH -v2.1] x86: Kill notsc Borislav Petkov <bp@alien8.de> - 2015-11-16 19:50 +0100
  Re: [RFC PATCH -v2.1] x86: Kill notsc Thomas Gleixner <tglx@linutronix.de> - 2015-11-16 22:30 +0100
    Re: [RFC PATCH -v2.1] x86: Kill notsc "H. Peter Anvin" <hpa@zytor.com> - 2015-11-17 06:10 +0100
      Re: [RFC PATCH -v2.1] x86: Kill notsc Borislav Petkov <bp@alien8.de> - 2015-11-17 10:00 +0100
        Re: [RFC PATCH -v2.1] x86: Kill notsc Thomas Gleixner <tglx@linutronix.de> - 2015-11-17 10:20 +0100
          Re: [RFC PATCH -v2.1] x86: Kill notsc Borislav Petkov <bp@alien8.de> - 2015-11-17 10:40 +0100
            Re: [RFC PATCH -v2.1] x86: Kill notsc Thomas Gleixner <tglx@linutronix.de> - 2015-11-17 11:10 +0100
              Re: [RFC PATCH -v2.1] x86: Kill notsc Borislav Petkov <bp@alien8.de> - 2015-11-17 12:20 +0100

csiph-web