From: Conor Dooley <conor.dooley@microchip.com>

Similarly to commit 022eb8ae8b5e ("ARM: 8938/1: kernel: initialize
broadcast hrtimer based clock event device"), RISC-V needs to initiate
hrtimer based broadcast clock event device before C3STOP can be used.
Otherwise, the introduction of C3STOP for the RISC-V arch timer in
commit 232ccac1bd9b ("clocksource/drivers/riscv: Events are stopped
during CPU suspend") leaves us without any broadcast timer registered.
This prevents the kernel from entering oneshot mode, which breaks timer
behaviour, for example clock_nanosleep().

A test app that sleeps each cpu for 6, 5, 4, 3 ms respectively, HZ=250
& C3STOP enabled, the sleep times are rounded up to the next jiffy:
== CPU: 1 ==      == CPU: 2 ==      == CPU: 3 ==      == CPU: 4 ==
Mean: 7.974992    Mean: 7.976534    Mean: 7.962591    Mean: 3.952179
Std Dev: 0.154374 Std Dev: 0.156082 Std Dev: 0.171018 Std Dev: 0.076193
Hi: 9.472000      Hi: 10.495000     Hi: 8.864000      Hi: 4.736000
Lo: 6.087000      Lo: 6.380000      Lo: 4.872000      Lo: 3.403000
Samples: 521      Samples: 521      Samples: 521      Samples: 521

Link: https://lore.kernel.org/linux-riscv/YzYTNQRxLr7Q9JR0@spud/
Fixes: 232ccac1bd9b ("clocksource/drivers/riscv: Events are stopped during CPU suspend")
Suggested-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
---
 arch/riscv/kernel/time.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
index 8217b0f67c6c..1cf21db4fcc7 100644
--- a/arch/riscv/kernel/time.c
+++ b/arch/riscv/kernel/time.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/of_clk.h>
+#include <linux/clockchips.h>
 #include <linux/clocksource.h>
 #include <linux/delay.h>
 #include <asm/sbi.h>
@@ -29,6 +30,8 @@ void __init time_init(void)
 
 	of_clk_init(NULL);
 	timer_probe();
+
+	tick_setup_hrtimer_broadcast();
 }
 
 void clocksource_arch_init(struct clocksource *cs)
-- 
2.34.1

On 1 December 2022 12:39:52 GMT, Anup Patel <apatel@ventanamicro.com> wrote:
>From: Conor Dooley <conor.dooley@microchip.com>
>
>Similarly to commit 022eb8ae8b5e ("ARM: 8938/1: kernel: initialize
>broadcast hrtimer based clock event device"), RISC-V needs to initiate
>hrtimer based broadcast clock event device before C3STOP can be used.
>Otherwise, the introduction of C3STOP for the RISC-V arch timer in
>commit 232ccac1bd9b ("clocksource/drivers/riscv: Events are stopped
>during CPU suspend") leaves us without any broadcast timer registered.
>This prevents the kernel from entering oneshot mode, which breaks timer
>behaviour, for example clock_nanosleep().
>
>A test app that sleeps each cpu for 6, 5, 4, 3 ms respectively, HZ=250
>& C3STOP enabled, the sleep times are rounded up to the next jiffy:
>== CPU: 1 ==      == CPU: 2 ==      == CPU: 3 ==      == CPU: 4 ==
>Mean: 7.974992    Mean: 7.976534    Mean: 7.962591    Mean: 3.952179
>Std Dev: 0.154374 Std Dev: 0.156082 Std Dev: 0.171018 Std Dev: 0.076193
>Hi: 9.472000      Hi: 10.495000     Hi: 8.864000      Hi: 4.736000
>Lo: 6.087000      Lo: 6.380000      Lo: 4.872000      Lo: 3.403000
>Samples: 521      Samples: 521      Samples: 521      Samples: 521
>
>Link: https://lore.kernel.org/linux-riscv/YzYTNQRxLr7Q9JR0@spud/
>Fixes: 232ccac1bd9b ("clocksource/drivers/riscv: Events are stopped during CPU suspend")
>Suggested-by: Samuel Holland <samuel@sholland.org>
>Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
>Reviewed-by: Samuel Holland <samuel@sholland.org>
>Acked-by: Palmer Dabbelt <palmer@rivosinc.com>

Huh, thought I replied already but I just have forgotten to...
Since you've added this patch to your series,  it needs your SoB appended.

Thanks,
Conor.

>---
> arch/riscv/kernel/time.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
>index 8217b0f67c6c..1cf21db4fcc7 100644
>--- a/arch/riscv/kernel/time.c
>+++ b/arch/riscv/kernel/time.c
>@@ -5,6 +5,7 @@
>  */
> 
> #include <linux/of_clk.h>
>+#include <linux/clockchips.h>
> #include <linux/clocksource.h>
> #include <linux/delay.h>
> #include <asm/sbi.h>
>@@ -29,6 +30,8 @@ void __init time_init(void)
> 
> 	of_clk_init(NULL);
> 	timer_probe();
>+
>+	tick_setup_hrtimer_broadcast();
> }
> 
> void clocksource_arch_init(struct clocksource *cs)