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.tatas...@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). 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.
