Hi Juergen,
On 12/12/2023 09:47, Juergen Gross wrote:
Allow 16 bits per cpu number, which is the limit imposed by
spinlock_tickets_t.
This will allow up to 65535 cpus, while increasing only the size of
recursive spinlocks in debug builds from 8 to 12 bytes.
Looking at arch/Kconfig, it looks like we are limiting NR_CPUS to
maximum 4096. So can you outline why we need this?
Just to be clear is I am not against this change, but alone it seems a
little bit odd to increase the size in debug when that limit can never
be reached (at least today).
Cheers,
Signed-off-by: Juergen Gross <jgr...@suse.com>
---
xen/common/spinlock.c | 1 +
xen/include/xen/spinlock.h | 18 +++++++++---------
2 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
index 296bcf33e6..ae7c7c2086 100644
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -481,6 +481,7 @@ int rspin_trylock(rspinlock_t *lock)
/* Don't allow overflow of recurse_cpu field. */
BUILD_BUG_ON(NR_CPUS > SPINLOCK_NO_CPU);
+ BUILD_BUG_ON(SPINLOCK_CPU_BITS > sizeof(lock->recurse_cpu) * 8);
BUILD_BUG_ON(SPINLOCK_RECURSE_BITS < 3);
check_lock(&lock->debug, true);
diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
index 87946965b2..d720778cc1 100644
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -7,16 +7,16 @@
#include <asm/system.h>
#include <asm/spinlock.h>
-#define SPINLOCK_CPU_BITS 12
+#define SPINLOCK_CPU_BITS 16
#ifdef CONFIG_DEBUG_LOCKS
union lock_debug {
- uint16_t val;
-#define LOCK_DEBUG_INITVAL 0xffff
+ uint32_t val;
+#define LOCK_DEBUG_INITVAL 0xffffffff
struct {
- uint16_t cpu:SPINLOCK_CPU_BITS;
-#define LOCK_DEBUG_PAD_BITS (14 - SPINLOCK_CPU_BITS)
- uint16_t :LOCK_DEBUG_PAD_BITS;
+ uint32_t cpu:SPINLOCK_CPU_BITS;
+#define LOCK_DEBUG_PAD_BITS (30 - SPINLOCK_CPU_BITS)
+ uint32_t :LOCK_DEBUG_PAD_BITS;
bool irq_safe:1;
bool unseen:1;
};
@@ -210,10 +210,10 @@ typedef struct spinlock {
typedef struct rspinlock {
spinlock_tickets_t tickets;
- uint16_t recurse_cpu:SPINLOCK_CPU_BITS;
+ uint16_t recurse_cpu;
#define SPINLOCK_NO_CPU ((1u << SPINLOCK_CPU_BITS) - 1)
-#define SPINLOCK_RECURSE_BITS (16 - SPINLOCK_CPU_BITS)
- uint16_t recurse_cnt:SPINLOCK_RECURSE_BITS;
+#define SPINLOCK_RECURSE_BITS 8
+ uint8_t recurse_cnt;
#define SPINLOCK_MAX_RECURSE ((1u << SPINLOCK_RECURSE_BITS) - 1)
union lock_debug debug;
#ifdef CONFIG_DEBUG_LOCK_PROFILE
--
Julien Grall
