[PATCHv5 0/3] enable nr_cpus for powerpc

[PATCHv5 0/3] enable nr_cpus for powerpc

[Pingfan Liu]

It is a long time since my last v4 [1].

The code has undergone great changes. The paca[] array has been
reorganized and indexed by paca_ptrs[], which dramatically decreases the
memory consumption even if there are many unpresent cpus in the middle.

However, reordering the logical cpu numbers can further decrease the
size of paca_ptrs[] in the kdump case. So I keep [1/3], which
rotate-shifts the cpu's sequence number in the device tree to obtain the
logical cpu id.

Patch [2-3/3] make efforts to decrease the nr_cpus to be less than or
equal to two.

[1]: https://lore.kernel.org/linuxppc-dev/1520829790-14029-1-git-send-email-kernelfans@gmail.com/

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Wen Xiong <wenxiong@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: kexec@lists.infradead.org
To: linuxppc-dev@lists.ozlabs.org

Pingfan Liu (3):
  powerpc/setup: Loosen the mapping between cpu logical id and its seq
    in dt
  powerpc/setup: Handle the case when boot_cpuid greater than nr_cpus
  powerpc/setup: alloc extra paca_ptrs to hold boot_cpuid

 arch/powerpc/kernel/paca.c         |  10 +--
 arch/powerpc/kernel/prom.c         |  26 ++++---
 arch/powerpc/kernel/setup-common.c | 106 ++++++++++++++++++++++++-----
 3 files changed, 111 insertions(+), 31 deletions(-)

-- 
2.31.1

[PATCHv5 1/3] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt

[Pingfan Liu]

*** Idea ***
For kexec -p, the boot cpu can be not the cpu0, this causes the problem
of allocating memory for paca_ptrs[]. However, in theory, there is no
requirement to assign cpu's logical id as its present sequence in the
device tree. But there is something like cpu_first_thread_sibling(),
which makes assumption on the mapping inside a core. Hence partially
loosening the mapping, i.e. unbind the mapping of core while keep the
mapping inside a core.

*** Implement ***
At this early stage, there are plenty of memory to utilize. Hence, this
patch allocates interim memory to link the cpu info on a list, then
reorder cpus by changing the list head. As a result, there is a rotate
shift between the sequence number in dt and the cpu logical number.

*** Result ***
After this patch, a boot-cpu's logical id will always be mapped into the
range [0,threads_per_core).

Besides this, at this phase, all threads in the boot core are forced to
be onlined. This restriction will be lifted in a later patch with
extra effort.

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Wen Xiong <wenxiong@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: kexec@lists.infradead.org
To: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/prom.c         | 23 ++++----
 arch/powerpc/kernel/setup-common.c | 87 +++++++++++++++++++++++-------
 2 files changed, 83 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 0b5878c3125b..72be75d4f003 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -331,8 +331,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	const __be32 *intserv;
 	int i, nthreads;
 	int len;
-	int found = -1;
-	int found_thread = 0;
+	bool found = false;
 
 	/* We are scanning "cpu" nodes only */
 	if (type == NULL || strcmp(type, "cpu") != 0)
@@ -355,8 +354,15 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	for (i = 0; i < nthreads; i++) {
 		if (be32_to_cpu(intserv[i]) ==
 			fdt_boot_cpuid_phys(initial_boot_params)) {
-			found = boot_cpu_count;
-			found_thread = i;
+			/*
+			 * always map the boot-cpu logical id into the
+			 * range of [0, thread_per_core)
+			 */
+			boot_cpuid = i;
+			found = true;
+			/* This works around the hole in paca_ptrs[]. */
+			if (nr_cpu_ids < nthreads)
+				nr_cpu_ids = nthreads;
 		}
 #ifdef CONFIG_SMP
 		/* logical cpu id is always 0 on UP kernels */
@@ -365,15 +371,14 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	}
 
 	/* Not the boot CPU */
-	if (found < 0)
+	if (!found)
 		return 0;
 
-	DBG("boot cpu: logical %d physical %d\n", found,
-	    be32_to_cpu(intserv[found_thread]));
-	boot_cpuid = found;
+	DBG("boot cpu: logical %d physical %d\n", boot_cpuid,
+	    be32_to_cpu(intserv[boot_cpuid]));
 
 	if (IS_ENABLED(CONFIG_PPC64))
-		boot_cpu_hwid = be32_to_cpu(intserv[found_thread]);
+		boot_cpu_hwid = be32_to_cpu(intserv[boot_cpuid]);
 
 	/*
 	 * PAPR defines "logical" PVR values for cpus that
diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index d2a446216444..a07af8de6674 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -36,6 +36,7 @@
 #include <linux/of_platform.h>
 #include <linux/hugetlb.h>
 #include <linux/pgtable.h>
+#include <linux/list.h>
 #include <asm/io.h>
 #include <asm/paca.h>
 #include <asm/processor.h>
@@ -427,6 +428,13 @@ static void __init cpu_init_thread_core_maps(int tpc)
 
 u32 *cpu_to_phys_id = NULL;
 
+struct interrupt_server_node {
+	struct list_head node;
+	bool	avail;
+	int	len;
+	__be32 *intserv;
+};
+
 /**
  * setup_cpu_maps - initialize the following cpu maps:
  *                  cpu_possible_mask
@@ -448,11 +456,16 @@ u32 *cpu_to_phys_id = NULL;
 void __init smp_setup_cpu_maps(void)
 {
 	struct device_node *dn;
-	int cpu = 0;
-	int nthreads = 1;
+	int shift = 0, cpu = 0;
+	int j, nthreads = 1;
+	int len;
+	struct interrupt_server_node *intserv_node, *n;
+	struct list_head *bt_node, head;
+	bool avail, found_boot_cpu = false;
 
 	DBG("smp_setup_cpu_maps()\n");
 
+	INIT_LIST_HEAD(&head);
 	cpu_to_phys_id = memblock_alloc(nr_cpu_ids * sizeof(u32),
 					__alignof__(u32));
 	if (!cpu_to_phys_id)
@@ -462,7 +475,6 @@ void __init smp_setup_cpu_maps(void)
 	for_each_node_by_type(dn, "cpu") {
 		const __be32 *intserv;
 		__be32 cpu_be;
-		int j, len;
 
 		DBG("  * %pOF...\n", dn);
 
@@ -482,29 +494,68 @@ void __init smp_setup_cpu_maps(void)
 			}
 		}
 
-		nthreads = len / sizeof(int);
-
-		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
-			bool avail;
+		avail = of_device_is_available(dn);
+		if (!avail)
+			avail = !of_property_match_string(dn,
+					"enable-method", "spin-table");
 
-			DBG("    thread %d -> cpu %d (hard id %d)\n",
-			    j, cpu, be32_to_cpu(intserv[j]));
 
-			avail = of_device_is_available(dn);
-			if (!avail)
-				avail = !of_property_match_string(dn,
-						"enable-method", "spin-table");
+		intserv_node = memblock_alloc(sizeof(struct interrupt_server_node) + len,
+					__alignof__(u32));
+		if (!intserv_node)
+			panic("%s: Failed to allocate %zu bytes align=0x%zx\n",
+				__func__,
+				sizeof(struct interrupt_server_node) + len,
+				__alignof__(u32));
+		intserv_node->intserv = (__be32 *)((char *)intserv_node +
+						sizeof(struct interrupt_server_node));
+		intserv_node->len = len;
+		memcpy(intserv_node->intserv, intserv, len);
+		intserv_node->avail = avail;
+		INIT_LIST_HEAD(&intserv_node->node);
+		list_add_tail(&intserv_node->node, &head);
+
+		if (!found_boot_cpu) {
+			nthreads = len / sizeof(int);
+			for (j = 0 ; j < nthreads; j++) {
+				if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
+					bt_node = &intserv_node->node;
+					found_boot_cpu = true;
+					/*
+					 * Record the round-shift between dt
+					 * seq and cpu logical number
+					 */
+					shift = cpu - j;
+					break;
+				}
+
+				cpu++;
+			}
+		}
 
+	}
+	cpu = 0;
+	list_del_init(&head);
+	/* Select the primary thread, the boot cpu's slibing, as the logic 0 */
+	list_add_tail(&head, bt_node);
+	pr_info("the round shift between dt seq and the cpu logic number: %d\n", shift);
+	list_for_each_entry(intserv_node, &head, node) {
+
+		avail = intserv_node->avail;
+		nthreads = intserv_node->len / sizeof(int);
+		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
 			set_cpu_present(cpu, avail);
 			set_cpu_possible(cpu, true);
-			cpu_to_phys_id[cpu] = be32_to_cpu(intserv[j]);
+			cpu_to_phys_id[cpu] = be32_to_cpu(intserv_node->intserv[j]);
+			DBG("    thread %d -> cpu %d (hard id %d)\n",
+			    j, cpu, be32_to_cpu(intserv[j]));
 			cpu++;
 		}
+	}
 
-		if (cpu >= nr_cpu_ids) {
-			of_node_put(dn);
-			break;
-		}
+	list_for_each_entry_safe(intserv_node, n, &head, node) {
+		len = sizeof(struct interrupt_server_node) + intserv_node->len;
+		memblock_free(intserv_node, len);
 	}
 
 	/* If no SMT supported, nthreads is forced to 1 */
-- 
2.31.1

[PATCHv5 2/3] powerpc/setup: Handle the case when boot_cpuid greater than nr_cpus

[Pingfan Liu]

If the boot_cpuid is smaller than nr_cpus, it requires extra effort to
ensure the boot_cpu is in cpu_present_mask. This can be achieved by
reserving the last quota for the boot cpu.

Note: the restriction on nr_cpus will be lifted with more effort in the
next patch

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Wen Xiong <wenxiong@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: kexec@lists.infradead.org
To: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index a07af8de6674..58a988c64dd2 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -456,8 +456,8 @@ struct interrupt_server_node {
 void __init smp_setup_cpu_maps(void)
 {
 	struct device_node *dn;
-	int shift = 0, cpu = 0;
-	int j, nthreads = 1;
+	int terminate, shift = 0, cpu = 0;
+	int j, bt_thread = 0, nthreads = 1;
 	int len;
 	struct interrupt_server_node *intserv_node, *n;
 	struct list_head *bt_node, head;
@@ -520,6 +520,7 @@ void __init smp_setup_cpu_maps(void)
 			for (j = 0 ; j < nthreads; j++) {
 				if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
 					bt_node = &intserv_node->node;
+					bt_thread = j;
 					found_boot_cpu = true;
 					/*
 					 * Record the round-shift between dt
@@ -539,11 +540,21 @@ void __init smp_setup_cpu_maps(void)
 	/* Select the primary thread, the boot cpu's slibing, as the logic 0 */
 	list_add_tail(&head, bt_node);
 	pr_info("the round shift between dt seq and the cpu logic number: %d\n", shift);
+	terminate = nr_cpu_ids;
 	list_for_each_entry(intserv_node, &head, node) {
 
+		j = 0;
+		/* Choose a start point to cover the boot cpu */
+		if (nr_cpu_ids - 1 < bt_thread) {
+			/*
+			 * The processor core puts assumption on the thread id,
+			 * not to breach the assumption.
+			 */
+			terminate = nr_cpu_ids - 1;
+		}
 		avail = intserv_node->avail;
 		nthreads = intserv_node->len / sizeof(int);
-		for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
+		for (; j < nthreads && cpu < terminate; j++) {
 			set_cpu_present(cpu, avail);
 			set_cpu_possible(cpu, true);
 			cpu_to_phys_id[cpu] = be32_to_cpu(intserv_node->intserv[j]);
@@ -551,6 +562,14 @@ void __init smp_setup_cpu_maps(void)
 			    j, cpu, be32_to_cpu(intserv[j]));
 			cpu++;
 		}
+		/* Online the boot cpu */
+		if (nr_cpu_ids - 1 < bt_thread) {
+			set_cpu_present(bt_thread, avail);
+			set_cpu_possible(bt_thread, true);
+			cpu_to_phys_id[bt_thread] = be32_to_cpu(intserv_node->intserv[bt_thread]);
+			DBG("    thread %d -> cpu %d (hard id %d)\n",
+			    bt_thread, bt_thread, be32_to_cpu(intserv[bt_thread]));
+		}
 	}
 
 	list_for_each_entry_safe(intserv_node, n, &head, node) {
-- 
2.31.1

[PATCHv5 3/3] powerpc/setup: alloc extra paca_ptrs to hold boot_cpuid

[Pingfan Liu]

paca_ptrs should be large enough to hold the boot_cpuid, hence, its
lower boundary is set to the bigger one between boot_cpuid+1 and
nr_cpus.

On the other hand, some kernel component: -1. the timer assumes cpu0
online since the timer_list->flags subfield 'TIMER_CPUMASK' is zero if
not initialized to a proper present cpu.  -2. power9_idle_stop() assumes
the primary thread's paca is allocated.

Hence lift nr_cpu_ids from one to two to ensure cpu0 is onlined, if the
boot cpu is not cpu0.

Signed-off-by: Pingfan Liu <piliu@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Wen Xiong <wenxiong@linux.ibm.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: kexec@lists.infradead.org
To: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/paca.c | 10 ++++++----
 arch/powerpc/kernel/prom.c |  9 ++++++---
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
index cda4e00b67c1..91e2401de1bd 100644
--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c
@@ -242,9 +242,10 @@ static int __initdata paca_struct_size;
 
 void __init allocate_paca_ptrs(void)
 {
-	paca_nr_cpu_ids = nr_cpu_ids;
+	int n = (boot_cpuid + 1) > nr_cpu_ids ? (boot_cpuid + 1) : nr_cpu_ids;
 
-	paca_ptrs_size = sizeof(struct paca_struct *) * nr_cpu_ids;
+	paca_nr_cpu_ids = n;
+	paca_ptrs_size = sizeof(struct paca_struct *) * n;
 	paca_ptrs = memblock_alloc_raw(paca_ptrs_size, SMP_CACHE_BYTES);
 	if (!paca_ptrs)
 		panic("Failed to allocate %d bytes for paca pointers\n",
@@ -287,13 +288,14 @@ void __init allocate_paca(int cpu)
 void __init free_unused_pacas(void)
 {
 	int new_ptrs_size;
+	int n = (boot_cpuid + 1) > nr_cpu_ids ? (boot_cpuid + 1) : nr_cpu_ids;
 
-	new_ptrs_size = sizeof(struct paca_struct *) * nr_cpu_ids;
+	new_ptrs_size = sizeof(struct paca_struct *) * n;
 	if (new_ptrs_size < paca_ptrs_size)
 		memblock_phys_free(__pa(paca_ptrs) + new_ptrs_size,
 				   paca_ptrs_size - new_ptrs_size);
 
-	paca_nr_cpu_ids = nr_cpu_ids;
+	paca_nr_cpu_ids = n;
 	paca_ptrs_size = new_ptrs_size;
 
 #ifdef CONFIG_PPC_64S_HASH_MMU
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 72be75d4f003..eca6a1568749 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -360,9 +360,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 			 */
 			boot_cpuid = i;
 			found = true;
-			/* This works around the hole in paca_ptrs[]. */
-			if (nr_cpu_ids < nthreads)
-				nr_cpu_ids = nthreads;
+			/*
+			 * Ideally, nr_cpus=1 can be achieved if each kernel
+			 * component does not assume cpu0 is onlined.
+			 */
+			if (boot_cpuid != 0 && nr_cpu_ids < 2)
+				nr_cpu_ids = 2;
 		}
 #ifdef CONFIG_SMP
 		/* logical cpu id is always 0 on UP kernels */
-- 
2.31.1

Re: [PATCHv5 1/3] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt

[kernel test robot]

Hi Pingfan,

kernel test robot noticed the following build errors:

[auto build test ERROR on powerpc/fixes]
[also build test ERROR on linus/master v6.5 next-20230908]
[cannot apply to powerpc/next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Pingfan-Liu/powerpc-setup-Loosen-the-mapping-between-cpu-logical-id-and-its-seq-in-dt/20230908-222430
base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git fixes
patch link:    https://lore.kernel.org/r/20230908141941.13660-2-piliu%40redhat.com
patch subject: [PATCHv5 1/3] powerpc/setup: Loosen the mapping between cpu logical id and its seq in dt
config: powerpc-allnoconfig (https://download.01.org/0day-ci/archive/20230908/202309082357.FUmBMhC4-lkp@intel.com/config)
compiler: powerpc-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230908/202309082357.FUmBMhC4-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309082357.FUmBMhC4-lkp@intel.com/

All errors (new ones prefixed by >>):

   arch/powerpc/kernel/prom.c: In function 'early_init_dt_scan_cpus':
   arch/powerpc/kernel/prom.c:365:44: error: lvalue required as left operand of assignment
     365 |                                 nr_cpu_ids = nthreads;
         |                                            ^
   arch/powerpc/kernel/prom.c: At top level:
>> arch/powerpc/kernel/prom.c:79:23: error: 'boot_cpu_count' defined but not used [-Werror=unused-variable]
      79 | static int __initdata boot_cpu_count;
         |                       ^~~~~~~~~~~~~~
   cc1: all warnings being treated as errors


vim +/boot_cpu_count +79 arch/powerpc/kernel/prom.c

c1e53367dab15e Srikar Dronamraju      2021-04-15  70  
9b6b563c0d2d25 Paul Mackerras         2005-10-06  71  #ifdef CONFIG_PPC64
28897731318dc8 Olof Johansson         2006-04-12  72  int __initdata iommu_is_off;
9b6b563c0d2d25 Paul Mackerras         2005-10-06  73  int __initdata iommu_force_on;
cf00a8d18b9a1c Paul Mackerras         2005-10-31  74  unsigned long tce_alloc_start, tce_alloc_end;
cd3db0c4ca3d23 Benjamin Herrenschmidt 2010-07-06  75  u64 ppc64_rma_size;
e13d23a404f2e6 Laurent Dufour         2022-11-10  76  unsigned int boot_cpu_node_count __ro_after_init;
9b6b563c0d2d25 Paul Mackerras         2005-10-06  77  #endif
03bf469add176a Benjamin Herrenschmidt 2011-05-11  78  static phys_addr_t first_memblock_size;
7ac87abb8166b9 Matt Evans             2011-05-25 @79  static int __initdata boot_cpu_count;
9b6b563c0d2d25 Paul Mackerras         2005-10-06  80  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki