| Message ID | 20240327152229.25847-7-jgross@suse.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | xen/spinlock: make recursive spinlocks a dedicated type | expand |
On 27.03.2024 16:22, 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. > > The current Xen limit of 4095 cpus is imposed by SPINLOCK_CPU_BITS > being 12. There are machines available with more cpus than the current > Xen limit, so it makes sense to have the possibility to use more cpus. > > Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> albeit I have to say that I'm not entirely convinced of ... > --- a/xen/common/spinlock.c > +++ b/xen/common/spinlock.c > @@ -485,7 +485,9 @@ bool _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); > + BUILD_BUG_ON(SPINLOCK_MAX_RECURSE > ((1u << SPINLOCK_RECURSE_BITS) - 1)); > > check_lock(&lock->debug, true); ... the two additions here: The two checks we had verify independent properties, whereas the new ones basically check that struct rspinlock and its associated #define-s were got right. We don't check such elsewhere, I don't think. Jan
On 02.04.24 16:42, Jan Beulich wrote: > On 27.03.2024 16:22, 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. >> >> The current Xen limit of 4095 cpus is imposed by SPINLOCK_CPU_BITS >> being 12. There are machines available with more cpus than the current >> Xen limit, so it makes sense to have the possibility to use more cpus. >> >> Signed-off-by: Juergen Gross <jgross@suse.com> > > Reviewed-by: Jan Beulich <jbeulich@suse.com> > albeit I have to say that I'm not entirely convinced of ... > >> --- a/xen/common/spinlock.c >> +++ b/xen/common/spinlock.c >> @@ -485,7 +485,9 @@ bool _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); >> + BUILD_BUG_ON(SPINLOCK_MAX_RECURSE > ((1u << SPINLOCK_RECURSE_BITS) - 1)); >> >> check_lock(&lock->debug, true); > > ... the two additions here: The two checks we had verify independent > properties, whereas the new ones basically check that struct rspinlock > and its associated #define-s were got right. We don't check such > elsewhere, I don't think. I think we do. What about: BUILD_BUG_ON(sizeof(hwp_req) != sizeof(hwp_req.raw)) checking that two union elements are of the same size (and both elements don't contain any other structs). Additionally it is not obvious at a first glance that SPINLOCK_CPU_BITS defined in line 11 is relevant for the definition of recurse_cpu in line 217. Regarding the second added BUILD_BUG_ON() there was a comment by Julien related to the definition of SPINLOCK_MAX_RECURSE in V4 of this patch. We settled to use the current form including the added BUILD_BUG_ON(). Juergen
diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c index 7ccb725171..5aa9ba6188 100644 --- a/xen/common/spinlock.c +++ b/xen/common/spinlock.c @@ -485,7 +485,9 @@ bool _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); + BUILD_BUG_ON(SPINLOCK_MAX_RECURSE > ((1u << SPINLOCK_RECURSE_BITS) - 1)); check_lock(&lock->debug, true); diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h index 3a4092626c..db00a24646 100644 --- a/xen/include/xen/spinlock.h +++ b/xen/include/xen/spinlock.h @@ -8,16 +8,16 @@ #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; + unsigned int cpu:SPINLOCK_CPU_BITS; +#define LOCK_DEBUG_PAD_BITS (30 - SPINLOCK_CPU_BITS) + unsigned int :LOCK_DEBUG_PAD_BITS; bool irq_safe:1; bool unseen:1; }; @@ -211,11 +211,11 @@ 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_MAX_RECURSE ((1u << SPINLOCK_RECURSE_BITS) - 1) +#define SPINLOCK_RECURSE_BITS 8 + uint8_t recurse_cnt; +#define SPINLOCK_MAX_RECURSE 15 union lock_debug debug; #ifdef CONFIG_DEBUG_LOCK_PROFILE struct lock_profile *profile;
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. The current Xen limit of 4095 cpus is imposed by SPINLOCK_CPU_BITS being 12. There are machines available with more cpus than the current Xen limit, so it makes sense to have the possibility to use more cpus. Signed-off-by: Juergen Gross <jgross@suse.com> --- V5: - keep previous recursion limit (Julien Grall) V6: - use unsigned int instead of uint32_t (Jan Beulich) --- xen/common/spinlock.c | 2 ++ xen/include/xen/spinlock.h | 20 ++++++++++---------- 2 files changed, 12 insertions(+), 10 deletions(-)