search for: __kvm_vcpu_is_preempted

...s reported by perf were as follows: 69.75% 0.59% fio [k] down_write 69.15% 0.01% fio [k] call_rwsem_down_write_failed 67.12% 1.12% fio [k] rwsem_down_write_failed 63.48% 52.77% fio [k] osq_lock 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted Making vcpu_is_preempted() a callee-save function has a relatively high cost on x86-64 primarily due to at least one more cacheline of data access from the saving and restoring of registers (8 of them) to and from stack as well as one more level of function call. As vcpu_is_preempted() is called w...

...s reported by perf were as follows: 69.75% 0.59% fio [k] down_write 69.15% 0.01% fio [k] call_rwsem_down_write_failed 67.12% 1.12% fio [k] rwsem_down_write_failed 63.48% 52.77% fio [k] osq_lock 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted Making vcpu_is_preempted() a callee-save function has a relatively high cost on x86-64 primarily due to at least one more cacheline of data access from the saving and restoring of registers (8 of them) to and from stack as well as one more level of function call. As vcpu_is_preempted() is called w...

...0.59% fio [k] down_write >> 69.15% 0.01% fio [k] call_rwsem_down_write_failed >> 67.12% 1.12% fio [k] rwsem_down_write_failed >> 63.48% 52.77% fio [k] osq_lock >> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt >> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted >> > Thinking about this again, wouldn't something like the below also work? > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 099fcba4981d..6aa33702c15c 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -589,6 +589,7 @@...

...0.59% fio [k] down_write >> 69.15% 0.01% fio [k] call_rwsem_down_write_failed >> 67.12% 1.12% fio [k] rwsem_down_write_failed >> 63.48% 52.77% fio [k] osq_lock >> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt >> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted >> > Thinking about this again, wouldn't something like the below also work? > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 099fcba4981d..6aa33702c15c 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -589,6 +589,7 @@...

...n_write >>> 69.15% 0.01% fio [k] call_rwsem_down_write_failed >>> 67.12% 1.12% fio [k] rwsem_down_write_failed >>> 63.48% 52.77% fio [k] osq_lock >>> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt >>> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted >>> >> Thinking about this again, wouldn't something like the below also work? >> >> >> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c >> index 099fcba4981d..6aa33702c15c 100644 >> --- a/arch/x86/kernel/kvm.c >> +++ b/arch/x86/kerne...

...s reported by perf were as follows: 69.75% 0.59% fio [k] down_write 69.15% 0.01% fio [k] call_rwsem_down_write_failed 67.12% 1.12% fio [k] rwsem_down_write_failed 63.48% 52.77% fio [k] osq_lock 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted Making vcpu_is_preempted() a callee-save function has a relatively high cost on x86-64 primarily due to at least one more cacheline of data access from the saving and restoring of registers (8 of them) to and from stack as well as one more level of function call. To reduce this performance overhe...

...s reported by perf were as follows: 69.75% 0.59% fio [k] down_write 69.15% 0.01% fio [k] call_rwsem_down_write_failed 67.12% 1.12% fio [k] rwsem_down_write_failed 63.48% 52.77% fio [k] osq_lock 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted Making vcpu_is_preempted() a callee-save function has a relatively high cost on x86-64 primarily due to at least one more cacheline of data access from the saving and restoring of registers (8 of them) to and from stack as well as one more level of function call. To reduce this performance overhe...

v3->v4: - Fix x86-32 build error. v2->v3: - Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted() in assembly as suggested by PeterZ. - Add a new patch to change vcpu_is_preempted() argument type to long to ease the writing of the assembly code. v1->v2: - Rerun the fio test on a different system on both bare-metal and a KVM guest. Both sockets were utilized in this test....

v3->v4: - Fix x86-32 build error. v2->v3: - Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted() in assembly as suggested by PeterZ. - Add a new patch to change vcpu_is_preempted() argument type to long to ease the writing of the assembly code. v1->v2: - Rerun the fio test on a different system on both bare-metal and a KVM guest. Both sockets were utilized in this test....

v2->v3: - Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted() in assembly as suggested by PeterZ. - Add a new patch to change vcpu_is_preempted() argument type to long to ease the writing of the assembly code. v1->v2: - Rerun the fio test on a different system on both bare-metal and a KVM guest. Both sockets were utilized in this test....

v2->v3: - Provide an optimized __raw_callee_save___kvm_vcpu_is_preempted() in assembly as suggested by PeterZ. - Add a new patch to change vcpu_is_preempted() argument type to long to ease the writing of the assembly code. v1->v2: - Rerun the fio test on a different system on both bare-metal and a KVM guest. Both sockets were utilized in this test....

...k on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 71.27% 0.28% fio [k] down_write 70.99% 0.01% fio [k] call_rwsem_down_write_failed 69.43% 1.18% fio [k] rwsem_down_write_failed 65.51% 54.57% fio [k] osq_lock 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted 4.16% 4.16% fio [k] __kvm_vcpu_is_preempted So making vcpu_is_preempted() a callee-save function has a pretty high cost associated with it. As vcpu_is_preempted() is called within the spinlock, mutex and rwsem slowpaths, there isn't much to gain by making it callee-save. So it is now chan...

...k on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 71.27% 0.28% fio [k] down_write 70.99% 0.01% fio [k] call_rwsem_down_write_failed 69.43% 1.18% fio [k] rwsem_down_write_failed 65.51% 54.57% fio [k] osq_lock 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted 4.16% 4.16% fio [k] __kvm_vcpu_is_preempted So making vcpu_is_preempted() a callee-save function has a pretty high cost associated with it. As vcpu_is_preempted() is called within the spinlock, mutex and rwsem slowpaths, there isn't much to gain by making it callee-save. So it is now chan...

...> > 69.75% 0.59% fio [k] down_write > 69.15% 0.01% fio [k] call_rwsem_down_write_failed > 67.12% 1.12% fio [k] rwsem_down_write_failed > 63.48% 52.77% fio [k] osq_lock > 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt > 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted > Thinking about this again, wouldn't something like the below also work? diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 099fcba4981d..6aa33702c15c 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val)...

..._time_ops.steal_clock = kvm_steal_clock; -#ifdef CONFIG_PARAVIRT_SPINLOCKS - pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted; -#endif } if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) @@ -604,6 +592,14 @@ static void kvm_wait(u8 *ptr, u8 val) local_irq_restore(flags); } +static bool __kvm_vcpu_is_preempted(int cpu) +{ + struct kvm_steal_time *src = &per_cpu(steal_time, cpu); + + return !!src->preempted; +} +PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); + /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */ @@ -620,6 +616,12 @@ void __init kvm_spinlock_init(void)...

..._time_ops.steal_clock = kvm_steal_clock; -#ifdef CONFIG_PARAVIRT_SPINLOCKS - pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted; -#endif } if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) @@ -604,6 +592,14 @@ static void kvm_wait(u8 *ptr, u8 val) local_irq_restore(flags); } +static bool __kvm_vcpu_is_preempted(int cpu) +{ + struct kvm_steal_time *src = &per_cpu(steal_time, cpu); + + return !!src->preempted; +} +PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); + /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */ @@ -620,6 +616,12 @@ void __init kvm_spinlock_init(void)...

On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: > It is the address of &steal_time that will exceed the 32-bit limit. That seems extremely unlikely. That would mean we have more than 4G worth of per-cpu variables declared in the kernel.

On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: > It is the address of &steal_time that will exceed the 32-bit limit. That seems extremely unlikely. That would mean we have more than 4G worth of per-cpu variables declared in the kernel.

On Fri, Feb 10, 2017 at 12:00:43PM -0500, Waiman Long wrote: > >> +asm( > >> +".pushsection .text;" > >> +".global __raw_callee_save___kvm_vcpu_is_preempted;" > >> +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;" > >> +"__raw_callee_save___kvm_vcpu_is_preempted:" > >> +FRAME_BEGIN > >> +"push %rdi;" > >> +"push %rdx;" > >> +"movslq %ed...

On Fri, Feb 10, 2017 at 12:00:43PM -0500, Waiman Long wrote: > >> +asm( > >> +".pushsection .text;" > >> +".global __raw_callee_save___kvm_vcpu_is_preempted;" > >> +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;" > >> +"__raw_callee_save___kvm_vcpu_is_preempted:" > >> +FRAME_BEGIN > >> +"push %rdi;" > >> +"push %rdx;" > >> +"movslq %ed...