Hi Pavel,
On Tue, Nov 20, 2018 at 09:43:40AM -0500, Pavel Tatashin wrote:
> Allow printk time stamps/sched_clock() to be available from the early
> boot.
>
> Signed-off-by: Pavel Tatashin <pasha.tatas...@soleen.com>
> ---
> arch/arm64/kernel/setup.c | 25 +++++++++++++++++++++++++
> drivers/clocksource/arm_arch_timer.c | 8 ++++----
> include/clocksource/arm_arch_timer.h | 3 +++
> 3 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index f4fc1e0544b7..7a43e63b737b 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -40,6 +40,7 @@
> #include <linux/efi.h>
> #include <linux/psci.h>
> #include <linux/sched/task.h>
> +#include <linux/sched_clock.h>
> #include <linux/mm.h>
>
> #include <asm/acpi.h>
> @@ -279,8 +280,32 @@ arch_initcall(reserve_memblock_reserved_regions);
>
> u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
>
> +/*
> + * Get time stamps available early in boot, useful to identify boot time
> issues
> + * from the early boot.
> + */
> +static __init void sched_clock_early_init(void)
> +{
> + u64 freq = arch_timer_get_cntfrq();
> +
> + /*
> + * The arm64 boot protocol mandates that CNTFRQ_EL0 reflects
> + * the timer frequency. To avoid breakage on misconfigured
> + * systems, do not register the early sched_clock if the
> + * programmed value if zero. Other random values will just
> + * result in random output.
> + */
> + if (!freq)
> + return;
> +
> + arch_timer_read_counter = arch_counter_get_cntvct;
Why do you need to assign this here?
> + sched_clock_register(arch_timer_read_counter, ARCH_TIMER_NBITS, freq);
arch_timer_read_counter can be reassigned once the arm_arch_timer driver
has probed; what stops this from being unused as the sched_clock after that
has happened? I worry that toggling the function pointer could lead to
sched_clock() going backwards.
> +}
> +
> void __init setup_arch(char **cmdline_p)
> {
> + sched_clock_early_init();
> +
> init_mm.start_code = (unsigned long) _text;
> init_mm.end_code = (unsigned long) _etext;
> init_mm.end_data = (unsigned long) _edata;
The patch from this point onwards just looks like a refactoring to me which
should be independent of adding early printk timestamps. Also, it doesn't
update the vdso logic, which hardwires a 56-bit mask for the counter values.
Will
> diff --git a/drivers/clocksource/arm_arch_timer.c
> b/drivers/clocksource/arm_arch_timer.c
> index 9a7d4dc00b6e..e4843ad48bd3 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -175,13 +175,13 @@ static struct clocksource clocksource_counter = {
> .name = "arch_sys_counter",
> .rating = 400,
> .read = arch_counter_read,
> - .mask = CLOCKSOURCE_MASK(56),
> + .mask = CLOCKSOURCE_MASK(ARCH_TIMER_NBITS),
> .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> };
>
> static struct cyclecounter cyclecounter __ro_after_init = {
> .read = arch_counter_read_cc,
> - .mask = CLOCKSOURCE_MASK(56),
> + .mask = CLOCKSOURCE_MASK(ARCH_TIMER_NBITS),
> };
>
> struct ate_acpi_oem_info {
> @@ -963,8 +963,8 @@ static void __init arch_counter_register(unsigned type)
> timecounter_init(&arch_timer_kvm_info.timecounter,
> &cyclecounter, start_count);
>
> - /* 56 bits minimum, so we assume worst case rollover */
> - sched_clock_register(arch_timer_read_counter, 56, arch_timer_rate);
> + sched_clock_register(arch_timer_read_counter, ARCH_TIMER_NBITS,
> + arch_timer_rate);
> }
>
> static void arch_timer_stop(struct clock_event_device *clk)
> diff --git a/include/clocksource/arm_arch_timer.h
> b/include/clocksource/arm_arch_timer.h
> index 349e5957c949..c485512e1d01 100644
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -71,6 +71,9 @@ enum arch_timer_spi_nr {
> #define ARCH_TIMER_EVT_STREAM_FREQ \
> (USEC_PER_SEC / ARCH_TIMER_EVT_STREAM_PERIOD_US)
>
> +/* 56 bits minimum, so we assume worst case rollover */
> +#define ARCH_TIMER_NBITS 56
> +
> struct arch_timer_kvm_info {
> struct timecounter timecounter;
> int virtual_irq;
> --
> 2.19.1
>
