Hi Bin,
On Sun, 28 Jun 2020 at 01:35, Bin Meng bmeng.cn@gmail.com wrote:
Hi Simon,
On Mon, Jun 15, 2020 at 1:00 AM Simon Glass sjg@chromium.org wrote:
It is convenient to iterate through the CPUs performing work on each one and processing the result. Add a few iterator functions which handle
this.
These can be used by any client code. It can call mp_run_on_cpus() on each CPU that is returned, handling them one at a time.
Signed-off-by: Simon Glass sjg@chromium.org Reviewed-by: Wolfgang Wallner wolfgang.wallner@br-automation.com
(no changes since v1)
arch/x86/cpu/mp_init.c | 62 +++++++++++++++++++++++++++++++++++++++ arch/x86/include/asm/mp.h | 40 +++++++++++++++++++++++++ 2 files changed, 102 insertions(+)
diff --git a/arch/x86/cpu/mp_init.c b/arch/x86/cpu/mp_init.c index 9970b51c8d..c708c3e3c0 100644 --- a/arch/x86/cpu/mp_init.c +++ b/arch/x86/cpu/mp_init.c @@ -675,6 +675,68 @@ int mp_park_aps(void) return get_timer(start); }
+int mp_first_cpu(int cpu_select) +{
struct udevice *dev;int num_cpus;int ret;/** This assumes that CPUs are numbered from 0. This function
tries to
* avoid assuming the CPU 0 is the boot CPUSo CPU 0 is not BSP ..
It does seem to be, but I worry that we might hit an architecture where it is not?
*/if (cpu_select == MP_SELECT_ALL)return 0; /* start with the first one */ret = get_bsp(&dev, &num_cpus);if (ret < 0)return log_msg_ret("bsp", ret);/* Return boot CPU if requested */if (cpu_select == MP_SELECT_BSP)return ret;/* Return something other than the boot CPU, if APs requested */if (cpu_select == MP_SELECT_APS && num_cpus > 1)return ret == 0 ? 1 : 0;/* Try to check for an invalid value */if (cpu_select < 0 || cpu_select >= num_cpus)The logic (cpu_select >= num_cpus) assumes that cpu number is consecutive.
Yes, 0...n-1 as set up by mp_init() using values from the device tree.
return -EINVAL;return cpu_select; /* return the only selected one */+}
+int mp_next_cpu(int cpu_select, int prev_cpu) +{
struct udevice *dev;int num_cpus;int ret;int bsp;/* If we selected the BSP or a particular single CPU, we are
done */
if (cpu_select == MP_SELECT_BSP || cpu_select >= 0)Why stops on MP_SELECT_BSP?
So if I call the 2 APIs with the following sequence, is this allowed?
int cpu = mp_first_cpu(MP_SELECT_ALL); // this will return zero cpu = mp_next_cpu(MP_SELECT_BSP, cpu); // then I got -EFBIG
No, you must provide the same value for cpu_select to both calls.
It does say that in the header file but I will add another note there.
return -EFBIG;/* Must be doing MP_SELECT_ALL or MP_SELECT_APS; return the
next CPU */
ret = get_bsp(&dev, &num_cpus);if (ret < 0)return log_msg_ret("bsp", ret);bsp = ret;/* Move to the next CPU */assert(prev_cpu >= 0);ret = prev_cpu + 1;/* Skip the BSP if needed */if (cpu_select == MP_SELECT_APS && ret == bsp)ret++;if (ret >= num_cpus)return -EFBIG;return ret;+}
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 38961ca44b..9f4223ae8c 100644 --- a/arch/x86/include/asm/mp.h +++ b/arch/x86/include/asm/mp.h @@ -115,6 +115,31 @@ int mp_run_on_cpus(int cpu_select, mp_run_func
func, void *arg);
- @return 0 on success, -ve on error
*/ int mp_park_aps(void);
+/**
- mp_first_cpu() - Get the first CPU to process, from a selection
- This is used to iterate through selected CPUs. Call this function
first, then
- call mp_next_cpu() repeatedly until it returns -EFBIG.
So how does specify the cpu_select of these 2 APIs? Do they have to be
the same?
For example, how about the following code sequence:
int cpu = mp_first_cpu(MP_SELECT_APS); cpu = mp_next_cpu(MP_SELECT_BSP, cpu); cpu = mp_next_cpu(MP_SELECT_APS, cpu);
It's quite ambiguous API design.
I will beef up the comments. cpu_select must be the same for all calls for the iteration to work.
- @cpu_select: Selected CPUs (either a CPU number or MP_SELECT_...)
- @return next CPU number to run on (e.g. 0)
- */
+int mp_first_cpu(int cpu_select);
+/**
- mp_next_cpu() - Get the next CPU to process, from a selection
- This is used to iterate through selected CPUs. After first calling
- mp_first_cpu() once, call this function repeatedly until it returns
-EFBIG.
- The value of @cpu_select must be the same for all calls.
- @cpu_select: Selected CPUs (either a CPU number or MP_SELECT_...)
Per the codes, if cpu_select >=0, -EFBIG will be returned. So this suggests that cpu_selct can only be MP_SELECT_APS?
mp_first_cpu() will return that CPU mp_next_cpu() will return -EFBIG of course, since the CPU has already run, so there is no 'next' CPU
I have to say that these 2 APIs are hard to understand ..
Think of the two functions as part of the same iterator.
Regards, SImon