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SubjectRe: [RFC 2/2] x86, tsc: Enable clock for ealry printk timestamp
On Wed, Jun 06, 2018 at 05:38:33PM +0800, Feng Tang wrote:
> On Sat, Jun 02, 2018 at 12:12:13AM +0800, Feng Tang wrote:
>
> Hi Peter and all,
>
>
> > Hi Peter and Petr,
> >
> > Thanks for your suggestions, will try to find a cleaner and less hacky way,
> > and it may take some time as dealing with all kinds of TSC is tricky :)
> >
> > - Feng
> >
> > On Thu, May 31, 2018 at 05:52:10PM +0200, Peter Zijlstra wrote:
> > > On Thu, May 31, 2018 at 03:55:42PM +0200, Petr Mladek wrote:
> > > > I wonder if we could get some cleaner integration into the timer and
> > > > printk code.
> > >
> > > Yes, these patches are particularly horrific..
> > >
> > > There were some earlier patches by Pavel Tatashin, which attempted do
> > > get things running earlier.
> > >
> > > http://lkml.kernel.org/r/20180209211143.16215-1-pasha.tatashin@oracle.com
> > >
> > > I'm not entirely happy with that, but I never did get around to
> > > reviewing that last version :-( In particuarly, now that you made me
> > > look, I dislike his patch 6 almost as much as these patches.
> > >
> > > The idea was to get regular sched_clock() running earlier, not to botch
> > > some early_sched_clock() into it.
> > >
> > > Basically run calibrate_tsc() earlier (like _waaay_ earlier, it doesn't
> > > rely on anything other than CPUID) and if you have a recent part (with
> > > exception of SKX) you'll get a usable tsc rate (and TSC_RELIABLE) and
> > > things will work.
>
>
> I just did a hacky experiment by moving the tsc_init()earlier into
> setup_arch() and remove the tsc_early_delay_calibrate(). The printk stamp
> does start working much earlier!
>
>
> But the __use_tsc and __sched_clock_stable are relying on jump_label,
> which can't be used so early (I tried to call the jump_label_init() before
> tsc_init(), but kernel crashs, and I worked around it for now).

Just figured out the kernel crash when taking jump_label_init() earlier
into setup_arch(), the tsc_init() will enable static_key __use_tsc

static_key_enable
__jump_label_update
arch_jump_label_transform
__jump_label_transform
text_poke_bp
text_poke

text_poke() will involve page , but paging is not initialized so
early yet, so it triggers a panic.

Beside this __use_tsc, the sched_clock also has one static key
__sched_clock_stable

Thanks,
Feng

>
> Please review the debug patch, thanks!
>
> ---
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 5c623df..b636888 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1201,7 +1201,8 @@ void __init setup_arch(char **cmdline_p)
> kvmclock_init();
> #endif
>
> - tsc_early_delay_calibrate();
> + tsc_init();
> +
> if (!early_xdbc_setup_hardware())
> early_xdbc_register_console();
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 4008dd6..8288f39 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -33,6 +33,7 @@ EXPORT_SYMBOL(cpu_khz);
> unsigned int __read_mostly tsc_khz;
> EXPORT_SYMBOL(tsc_khz);
>
> +int tsc_inited;
> /*
> * TSC can be unstable due to cpufreq or due to unsynced TSCs
> */
> @@ -192,7 +193,7 @@ static void set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long tsc_
> */
> u64 native_sched_clock(void)
> {
> - if (static_branch_likely(&__use_tsc)) {
> + if (static_branch_likely(&__use_tsc) || tsc_inited) {
> u64 tsc_now = rdtsc();
>
> /* return the value in ns */
> @@ -1387,30 +1391,16 @@ static int __init init_tsc_clocksource(void)
> */
> device_initcall(init_tsc_clocksource);
>
> -void __init tsc_early_delay_calibrate(void)
> -{
> - unsigned long lpj;
> -
> - if (!boot_cpu_has(X86_FEATURE_TSC))
> - return;
> -
> - cpu_khz = x86_platform.calibrate_cpu();
> - tsc_khz = x86_platform.calibrate_tsc();
> -
> - tsc_khz = tsc_khz ? : cpu_khz;
> - if (!tsc_khz)
> - return;
> -
> - lpj = tsc_khz * 1000;
> - do_div(lpj, HZ);
> - loops_per_jiffy = lpj;
> -}
> -
> void __init tsc_init(void)
> {
> u64 lpj, cyc;
> int cpu;
>
> + if (tsc_inited)
> + return;
> +
> + tsc_inited = 1;
> +
> if (!boot_cpu_has(X86_FEATURE_TSC)) {
> setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
> return;
> @@ -1474,11 +1464,15 @@ void __init tsc_init(void)
> lpj = ((u64)tsc_khz * 1000);
> do_div(lpj, HZ);
> lpj_fine = lpj;
> + loops_per_jiffy = lpj;
>
> use_tsc_delay();
>
> check_system_tsc_reliable();
>
> + extern void early_set_sched_clock_stable(u64 sched_clock_offset);
> + early_set_sched_clock_stable(div64_u64(rdtsc() * 1000, tsc_khz));
> +
> if (unsynchronized_tsc()) {
> mark_tsc_unstable("TSCs unsynchronized");
> return;
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index 10c83e7..6c5c22d 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -119,6 +119,13 @@ static void __scd_stamp(struct sched_clock_data *scd)
> scd->tick_raw = sched_clock();
> }
>
> +
> +void early_set_sched_clock_stable(u64 sched_clock_offset)
> +{
> + __sched_clock_offset = sched_clock_offset;
> + static_branch_enable(&__sched_clock_stable);
> +}
> +
> static void __set_sched_clock_stable(void)
> {
> struct sched_clock_data *scd;
> @@ -342,12 +349,14 @@ static u64 sched_clock_remote(struct sched_clock_data *scd)
> *
> * See cpu_clock().
> */
> +
> +extern int tsc_inited;
> u64 sched_clock_cpu(int cpu)
> {
> struct sched_clock_data *scd;
> u64 clock;
>
> - if (sched_clock_stable())
> + if (sched_clock_stable() || tsc_inited)
> return sched_clock() + __sched_clock_offset;
>
> if (unlikely(!sched_clock_running))
>
>
>
>
> > >
> > > If you have a dodgy part (sorry SKX), you'll just have to live with
> > > sched_clock starting late(r).
> > >
> > > Do not cobble things on the side, try and get the normal things running
> > > earlier.

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