Re: [PATCH v2 2/4] powerpc/spinlock: support vcpu preempted check
flat view
From: Balbir Singh <bsingharora@gmail.com>
Date: 2016-07-06 10:54:05
Also in:
linux-s390, lkml, virtualization
On Tue, 2016-06-28 at 10:43 -0400, Pan Xinhui wrote:
This is to fix some lock holder preemption issues. Some other locks implementation do a spin loop before acquiring the lock itself. Currently kernel has an interface of bool vcpu_is_preempted(int cpu). It take the cpu
^^ takes
as parameter and return true if the cpu is preempted. Then kernel can break the spin loops upon on the retval of vcpu_is_preempted. As kernel has used this interface, So lets support it. Only pSeries need supoort it. And the fact is powerNV are built into same
^^ support
kernel image with pSeries. So we need return false if we are runnig as powerNV. The another fact is that lppaca->yiled_count keeps zero on
^^ yield
quoted hunk ↗ jump to hunk
powerNV. So we can just skip the machine type. Suggested-by: Boqun Feng <redacted> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Pan Xinhui <redacted> --- arch/powerpc/include/asm/spinlock.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h index 523673d..3ac9fcb 100644 --- a/arch/powerpc/include/asm/spinlock.h +++ b/arch/powerpc/include/asm/spinlock.h@@ -52,6 +52,24 @@#define SYNC_IO #endif +/* + * This support kernel to check if one cpu is preempted or not. + * Then we can fix some lock holder preemption issue. + */ +#ifdef CONFIG_PPC_PSERIES +#define vcpu_is_preempted vcpu_is_preempted +static inline bool vcpu_is_preempted(int cpu) +{ + /* + * pSeries and powerNV can be built into same kernel image. In + * principle we need return false directly if we are running as + * powerNV. However the yield_count is always zero on powerNV, So + * skip such machine type check
Or you could use the ppc_md interface callbacks if required, but your solution works as well
+ */
+ return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1);
+}
+#endif
+
static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return lock.slock == 0;Balbir Singh.