Re: [PATCH v6 3/3] powerpc/powernv: Introduce sysfs control for fastsleep workaround behavior

From: Preeti U Murthy
Date: Mon Apr 20 2015 - 04:10:27 EST

On 04/20/2015 10:32 AM, Shreyas B. Prabhu wrote:
> Fastsleep is one of the idle state which cpuidle subsystem currently
> uses on power8 machines. In this state L2 cache is brought down to a
> threshold voltage. Therefore when the core is in fastsleep, the
> communication between L2 and L3 needs to be fenced. But there is a bug
> in the current power8 chips surrounding this fencing.
>
> OPAL provides a workaround which precludes the possibility of hitting
> this bug. But running with this workaround applied causes checkstop
> if any correctable error in L2 cache directory is detected. Hence OPAL
> also provides a way to undo the workaround.
>
> In the existing implementation, workaround is applied by the last thread
> of the core entering fastsleep and undone by the first thread waking up.
> But this has a performance cost. These OPAL calls account for roughly
> 4000 cycles everytime the core has to enter or wakeup from fastsleep.
>
> This patch introduces a sysfs attribute (fastsleep_workaround_applyonce)
> to choose the behavior of this workaround.
>
> By default, fastsleep_workaround_applyonce = 0. In this case, workaround
> is applied/undone everytime the core enters/exits fastsleep.
>
> fastsleep_workaround_applyonce = 1. In this case the workaround is
> applied once on all the cores and never undone. This can be triggered by
> echo 1 > /sys/devices/system/cpu/fastsleep_workaround_applyonce
>
> For simplicity this attribute can be modified only once. Implying, once
> fastsleep_workaround_applyonce is changed to 1, it cannot be reverted
> to the default state.
>
> Signed-off-by: Shreyas B. Prabhu <shreyas@xxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/include/asm/opal-api.h | 7 ++
> arch/powerpc/include/asm/opal.h | 1 +
> arch/powerpc/platforms/powernv/idle.c | 101 +++++++++++++++++++++++++
> arch/powerpc/platforms/powernv/opal-wrappers.S | 1 +
> 4 files changed, 110 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
> index 0321a90..a49e5fa 100644
> --- a/arch/powerpc/include/asm/opal-api.h
> +++ b/arch/powerpc/include/asm/opal-api.h
> @@ -165,6 +165,13 @@
> #define OPAL_PM_WINKLE_ENABLED 0x00040000
> #define OPAL_PM_SLEEP_ENABLED_ER1 0x00080000 /* with workaround */
>
> +/*
> + * OPAL_CONFIG_CPU_IDLE_STATE parameters
> + */
> +#define OPAL_CONFIG_IDLE_FASTSLEEP 1
> +#define OPAL_CONFIG_IDLE_UNDO 0
> +#define OPAL_CONFIG_IDLE_APPLY 1
> +
> #ifndef __ASSEMBLY__
>
> /* Other enums */
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index 042af1a..9a47813 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -186,6 +186,7 @@ int64_t opal_handle_hmi(void);
> int64_t opal_register_dump_region(uint32_t id, uint64_t start, uint64_t end);
> int64_t opal_unregister_dump_region(uint32_t id);
> int64_t opal_slw_set_reg(uint64_t cpu_pir, uint64_t sprn, uint64_t val);
> +int64_t opal_config_cpu_idle_state(uint64_t state, uint64_t flag);
> int64_t opal_pci_set_phb_cxl_mode(uint64_t phb_id, uint64_t mode, uint64_t pe_number);
> int64_t opal_ipmi_send(uint64_t interface, struct opal_ipmi_msg *msg,
> uint64_t msg_len);
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 104235a..f90cc86 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -13,6 +13,8 @@
> #include <linux/mm.h>
> #include <linux/slab.h>
> #include <linux/of.h>
> +#include <linux/device.h>
> +#include <linux/cpu.h>
>
> #include <asm/firmware.h>
> #include <asm/opal.h>
> @@ -136,6 +138,96 @@ u32 pnv_get_supported_cpuidle_states(void)
> }
> EXPORT_SYMBOL_GPL(pnv_get_supported_cpuidle_states);
>
> +
> +static void pnv_fastsleep_workaround_apply(void *info)
> +
> +{
> + int rc;
> + int *err = info;
> +
> + rc = opal_config_cpu_idle_state(OPAL_CONFIG_IDLE_FASTSLEEP,
> + OPAL_CONFIG_IDLE_APPLY);
> + if (rc)
> + *err = 1;
> +}
> +
> +/*
> + * Used to store fastsleep workaround state
> + * 0 - Workaround applied/undone at fastsleep entry/exit path (Default)
> + * 1 - Workaround applied once, never undone.
> + */
> +static u8 fastsleep_workaround_applyonce;
> +
> +static ssize_t show_fastsleep_workaround_applyonce(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%u\n", fastsleep_workaround_applyonce);
> +}
> +
> +static ssize_t store_fastsleep_workaround_applyonce(struct device *dev,
> + struct device_attribute *attr, const char *buf,
> + size_t count)
> +{
> + cpumask_t primary_thread_mask;
> + int err;
> + u8 val;
> +
> + if (kstrtou8(buf, 0, &val) || val != 1)
> + return -EINVAL;
> +
> + if (fastsleep_workaround_applyonce == 1)
> + return count;
> +
> + /*
> + * fastsleep_workaround_applyonce = 1 implies
> + * fastsleep workaround needs to be left in 'applied' state on all
> + * the cores. Do this by-
> + * 1. Patching out the call to 'undo' workaround in fastsleep exit path
> + * 2. Sending ipi to all the cores which have atleast one online thread
> + * 3. Patching out the call to 'apply' workaround in fastsleep entry
> + * path
> + * There is no need to send ipi to cores which have all threads
> + * offlined, as last thread of the core entering fastsleep or deeper
> + * state would have applied workaround.
> + */
> + err = patch_instruction(
> + (unsigned int *)pnv_fastsleep_workaround_at_exit,
> + PPC_INST_NOP);
> + if (err) {
> + pr_err("fastsleep_workaround_applyonce change failed while patching pnv_fastsleep_workaround_at_exit");
> + goto fail;
> + }
> +
> + get_online_cpus();
> + primary_thread_mask = cpu_online_cores_map();
> + on_each_cpu_mask(&primary_thread_mask,
> + pnv_fastsleep_workaround_apply,
> + &err, 1);
> + put_online_cpus();
> + if (err) {
> + pr_err("fastsleep_workaround_applyonce change failed while running pnv_fastsleep_workaround_apply");
> + goto fail;
> + }
> +
> + err = patch_instruction(
> + (unsigned int *)pnv_fastsleep_workaround_at_entry,
> + PPC_INST_NOP);
> + if (err) {
> + pr_err("fastsleep_workaround_applyonce change failed while patching pnv_fastsleep_workaround_at_entry");
> + goto fail;
> + }
> +
> + fastsleep_workaround_applyonce = 1;
> +
> + return count;
> +fail:
> + return -EIO;
> +}
> +
> +static DEVICE_ATTR(fastsleep_workaround_applyonce, 0600,
> + show_fastsleep_workaround_applyonce,
> + store_fastsleep_workaround_applyonce);
> +
> static int __init pnv_init_idle_states(void)
> {
> struct device_node *power_mgt;
> @@ -180,7 +272,16 @@ static int __init pnv_init_idle_states(void)
> patch_instruction(
> (unsigned int *)pnv_fastsleep_workaround_at_exit,
> PPC_INST_NOP);
> + } else {
> + /*
> + * OPAL_PM_SLEEP_ENABLED_ER1 is set. It indicates that
> + * workaround is needed to use fastsleep. Provide sysfs
> + * control to choose how this workaround has to be applied.
> + */
> + device_create_file(cpu_subsys.dev_root,
> + &dev_attr_fastsleep_workaround_applyonce);
> }
> +
> pnv_alloc_idle_core_states();
> out_free:
> kfree(flags);
> diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S b/arch/powerpc/platforms/powernv/opal-wrappers.S
> index a7ade94..bf15ead 100644
> --- a/arch/powerpc/platforms/powernv/opal-wrappers.S
> +++ b/arch/powerpc/platforms/powernv/opal-wrappers.S
> @@ -283,6 +283,7 @@ OPAL_CALL(opal_sensor_read, OPAL_SENSOR_READ);
> OPAL_CALL(opal_get_param, OPAL_GET_PARAM);
> OPAL_CALL(opal_set_param, OPAL_SET_PARAM);
> OPAL_CALL(opal_handle_hmi, OPAL_HANDLE_HMI);
> +OPAL_CALL(opal_config_cpu_idle_state, OPAL_CONFIG_CPU_IDLE_STATE);
> OPAL_CALL(opal_slw_set_reg, OPAL_SLW_SET_REG);
> OPAL_CALL(opal_register_dump_region, OPAL_REGISTER_DUMP_REGION);
> OPAL_CALL(opal_unregister_dump_region, OPAL_UNREGISTER_DUMP_REGION);
>

Reviewed-by: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>

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