[PATCH v4 13/25] x86: mp: Allow running functions on multiple CPUs
Bin Meng
bmeng.cn at gmail.com
Mon Jul 13 06:56:37 CEST 2020
Hi Simon,
On Wed, Jul 8, 2020 at 9:37 AM Simon Glass <sjg at chromium.org> wrote:
>
> Add a way to run a function on a selection of CPUs. This supports either
> a single CPU, all CPUs, just the main CPU or just the 'APs', in Intel
> terminology.
>
> It works by writing into a mailbox and then waiting for the CPUs to notice
> it, take action and indicate they are done.
>
> When SMP is not yet enabled, this just calls the function on the main CPU.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> Reviewed-by: Wolfgang Wallner <wolfgang.wallner at br-automation.com>
> ---
>
> Changes in v4:
> - Only enable this feature of CONFIG_SMP_AP_WORK is enabled
> - Allow running on the BSP if SMP is not enabled
>
> Changes in v3:
> - Add a comment to run_ap_work()
> - Rename flag to GD_FLG_SMP_READY
> - Update the comment for run_ap_work() to explain logical_cpu_number
> - Clarify meaning of @cpu_select in mp_run_on_cpus() comment
>
> arch/x86/cpu/mp_init.c | 107 +++++++++++++++++++++++++++++++++++---
> arch/x86/include/asm/mp.h | 33 ++++++++++++
> 2 files changed, 134 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/cpu/mp_init.c b/arch/x86/cpu/mp_init.c
> index 69a23829b9..dd6d6bfab7 100644
> --- a/arch/x86/cpu/mp_init.c
> +++ b/arch/x86/cpu/mp_init.c
> @@ -54,12 +54,7 @@ struct mp_flight_plan {
> * callback
> */
> struct mp_callback {
> - /**
> - * func() - Function to call on the AP
> - *
> - * @arg: Argument to pass
> - */
> - void (*func)(void *arg);
> + mp_run_func func;
> void *arg;
> int logical_cpu_number;
> };
> @@ -514,6 +509,70 @@ static void store_callback(struct mp_callback **slot, struct mp_callback *val)
> dmb();
> }
>
> +/**
> + * run_ap_work() - Run a callback on selected APs
> + *
> + * This writes @callback to all APs and waits for them all to acknowledge it,
> + * Note that whether each AP actually calls the callback depends on the value
> + * of logical_cpu_number (see struct mp_callback). The logical CPU number is
> + * the CPU device's req->seq value.
> + *
> + * @callback: Callback information to pass to all APs
> + * @bsp: CPU device for the BSP
> + * @num_cpus: The number of CPUs in the system (= number of APs + 1)
> + * @expire_ms: Timeout to wait for all APs to finish, in milliseconds, or 0 for
> + * no timeout
> + * @return 0 if OK, -ETIMEDOUT if one or more APs failed to respond in time
> + */
> +static int run_ap_work(struct mp_callback *callback, struct udevice *bsp,
> + int num_cpus, uint expire_ms)
> +{
> + int cur_cpu = bsp->req_seq;
> + int num_aps = num_cpus - 1; /* number of non-BSPs to get this message */
> + int cpus_accepted;
> + ulong start;
> + int i;
> +
> + if (!IS_ENABLED(CONFIG_SMP_AP_WORK)) {
> + printf("APs already parked. CONFIG_SMP_AP_WORK not enabled\n");
> + return -ENOTSUPP;
> + }
> +
> + /* Signal to all the APs to run the func. */
> + for (i = 0; i < num_cpus; i++) {
> + if (cur_cpu != i)
> + store_callback(&ap_callbacks[i], callback);
> + }
> + mfence();
> +
> + /* Wait for all the APs to signal back that call has been accepted. */
> + start = get_timer(0);
> +
> + do {
> + mdelay(1);
> + cpus_accepted = 0;
> +
> + for (i = 0; i < num_cpus; i++) {
> + if (cur_cpu == i)
> + continue;
> + if (!read_callback(&ap_callbacks[i]))
> + cpus_accepted++;
It looks my previous comments were not addressed. I believe there is a
bug here that cpus_accepted will double count for the 2nd time in the
do {} while () loop.
> + }
> +
> + if (expire_ms && get_timer(start) >= expire_ms) {
> + log(UCLASS_CPU, LOGL_CRIT,
> + "AP call expired; %d/%d CPUs accepted\n",
> + cpus_accepted, num_aps);
> + return -ETIMEDOUT;
> + }
> + } while (cpus_accepted != num_aps);
> +
> + /* Make sure we can see any data written by the APs */
> + mfence();
> +
> + return 0;
> +}
> +
> /**
> * ap_wait_for_instruction() - Wait for and process requests from the main CPU
> *
> @@ -573,6 +632,42 @@ static struct mp_flight_record mp_steps[] = {
> MP_FR_BLOCK_APS(ap_wait_for_instruction, NULL, NULL, NULL),
> };
>
> +int mp_run_on_cpus(int cpu_select, mp_run_func func, void *arg)
> +{
> + struct mp_callback lcb = {
> + .func = func,
> + .arg = arg,
> + .logical_cpu_number = cpu_select,
> + };
> + struct udevice *dev;
> + int num_cpus;
> + int ret;
> +
> + ret = get_bsp(&dev, &num_cpus);
> + if (ret < 0)
> + return log_msg_ret("bsp", ret);
> + if (cpu_select == MP_SELECT_ALL || cpu_select == MP_SELECT_BSP ||
> + cpu_select == ret) {
> + /* Run on BSP first */
> + func(arg);
> + }
> +
> + if (!IS_ENABLED(CONFIG_SMP_AP_WORK) ||
> + !(gd->flags & GD_FLG_SMP_READY)) {
> + /* Allow use of this function on the BSP only */
> + if (cpu_select == MP_SELECT_BSP || !cpu_select)
> + return 0;
> + return -ENOTSUPP;
> + }
> +
> + /* Allow up to 1 second for all APs to finish */
> + ret = run_ap_work(&lcb, dev, num_cpus, 1000 /* ms */);
> + if (ret)
> + return log_msg_ret("aps", ret);
> +
> + return 0;
> +}
> +
> int mp_init(void)
> {
> int num_aps, num_cpus;
> diff --git a/arch/x86/include/asm/mp.h b/arch/x86/include/asm/mp.h
> index 41b1575f4b..eb49e690f2 100644
> --- a/arch/x86/include/asm/mp.h
> +++ b/arch/x86/include/asm/mp.h
> @@ -86,4 +86,37 @@ int mp_init(void);
> /* Set up additional CPUs */
> int x86_mp_init(void);
>
> +/**
> + * mp_run_func() - Function to call on the AP
> + *
> + * @arg: Argument to pass
> + */
> +typedef void (*mp_run_func)(void *arg);
> +
> +#if defined(CONFIG_SMP) && !CONFIG_IS_ENABLED(X86_64)
> +/**
> + * mp_run_on_cpus() - Run a function on one or all CPUs
> + *
> + * This does not return until all CPUs have completed the work
> + *
> + * Running on anything other than the boot CPU is only supported if
> + * CONFIG_SMP_AP_WORK is enabled
> + *
> + * @cpu_select: CPU to run on (its dev->req_seq value), or MP_SELECT_ALL for
> + * all, or MP_SELECT_BSP for BSP
> + * @func: Function to run
> + * @arg: Argument to pass to the function
> + * @return 0 on success, -ve on error
> + */
> +int mp_run_on_cpus(int cpu_select, mp_run_func func, void *arg);
> +#else
> +static inline int mp_run_on_cpus(int cpu_select, mp_run_func func, void *arg)
> +{
> + /* There is only one CPU, so just call the function here */
> + func(arg);
> +
> + return 0;
> +}
> +#endif
> +
> #endif /* _X86_MP_H_ */
Regards,
Bin
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