search for: steal_tim

...ee_save___kvm_vcpu_is_preempted, @function;" > >> +"__raw_callee_save___kvm_vcpu_is_preempted:" > >> +FRAME_BEGIN > >> +"push %rdi;" > >> +"push %rdx;" > >> +"movslq %edi, %rdi;" > >> +"movq $steal_time+16, %rax;" > >> +"movq __per_cpu_offset(,%rdi,8), %rdx;" > >> +"cmpb $0, (%rdx,%rax);" Could we not put the $steal_time+16 displacement as an immediate in the cmpb and save a whole register here? That way we'd end up with something like: asm(...

...ee_save___kvm_vcpu_is_preempted, @function;" > >> +"__raw_callee_save___kvm_vcpu_is_preempted:" > >> +FRAME_BEGIN > >> +"push %rdi;" > >> +"push %rdx;" > >> +"movslq %edi, %rdi;" > >> +"movq $steal_time+16, %rax;" > >> +"movq __per_cpu_offset(,%rdi,8), %rdx;" > >> +"cmpb $0, (%rdx,%rax);" Could we not put the $steal_time+16 displacement as an immediate in the cmpb and save a whole register here? That way we'd end up with something like: asm(...

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.

...3702c15c 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) > local_irq_restore(flags); > } > > +#ifdef CONFIG_X86_32 > __visible bool __kvm_vcpu_is_preempted(int cpu) > { > struct kvm_steal_time *src = &per_cpu(steal_time, cpu); > @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) > } > PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); > > +#else > + > +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int); > + > +asm( > +&quo...

...3702c15c 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) > local_irq_restore(flags); > } > > +#ifdef CONFIG_X86_32 > __visible bool __kvm_vcpu_is_preempted(int cpu) > { > struct kvm_steal_time *src = &per_cpu(steal_time, cpu); > @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) > } > PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); > > +#else > + > +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int); > + > +asm( > +&quo...

...t; > >>> push %rdi; > >>> movslq %edi, %rdi; > >>> movq __per_cpu_offset(,%rdi,8), %rax; > >>> cmpb $0, %[offset](%rax); > >>> setne %al; > >>> pop %rdi; > >>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); > >>> > >>> And if we could get rid of the sign extend on edi we could avoid all the > >>> push-pop nonsense, but I'm not sure I see how to do that (then again, > >>> this asm foo isn't my stronges...

...t; > >>> push %rdi; > >>> movslq %edi, %rdi; > >>> movq __per_cpu_offset(,%rdi,8), %rax; > >>> cmpb $0, %[offset](%rax); > >>> setne %al; > >>> pop %rdi; > >>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); > >>> > >>> And if we could get rid of the sign extend on edi we could avoid all the > >>> push-pop nonsense, but I'm not sure I see how to do that (then again, > >>> this asm foo isn't my stronges...

...we'd end up with something like: >> >> asm(" >> push %rdi; >> movslq %edi, %rdi; >> movq __per_cpu_offset(,%rdi,8), %rax; >> cmpb $0, %[offset](%rax); >> setne %al; >> pop %rdi; >> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); >> >> And if we could get rid of the sign extend on edi we could avoid all the >> push-pop nonsense, but I'm not sure I see how to do that (then again, >> this asm foo isn't my strongest point). > Maybe: > > movs...

...we'd end up with something like: >> >> asm(" >> push %rdi; >> movslq %edi, %rdi; >> movq __per_cpu_offset(,%rdi,8), %rax; >> cmpb $0, %[offset](%rax); >> setne %al; >> pop %rdi; >> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); >> >> And if we could get rid of the sign extend on edi we could avoid all the >> push-pop nonsense, but I'm not sure I see how to do that (then again, >> this asm foo isn't my strongest point). > Maybe: > > movs...

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

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

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. - The commit log was

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. - The commit log was

...e'd end up with something like: >> >> asm(" >> push %rdi; >> movslq %edi, %rdi; >> movq __per_cpu_offset(,%rdi,8), %rax; >> cmpb $0, %[offset](%rax); >> setne %al; >> pop %rdi; >> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct >steal_time, preempted))); >> >> And if we could get rid of the sign extend on edi we could avoid all >the >> push-pop nonsense, but I'm not sure I see how to do that (then again, >> this asm foo isn't my strongest point). > >Maybe: &...

...e'd end up with something like: >> >> asm(" >> push %rdi; >> movslq %edi, %rdi; >> movq __per_cpu_offset(,%rdi,8), %rax; >> cmpb $0, %[offset](%rax); >> setne %al; >> pop %rdi; >> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct >steal_time, preempted))); >> >> And if we could get rid of the sign extend on edi we could avoid all >the >> push-pop nonsense, but I'm not sure I see how to do that (then again, >> this asm foo isn't my strongest point). > >Maybe: &...

...kernel/kvm.c >> +++ b/arch/x86/kernel/kvm.c >> @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val) >> local_irq_restore(flags); >> } >> >> +#ifdef CONFIG_X86_32 >> __visible bool __kvm_vcpu_is_preempted(int cpu) >> { >> struct kvm_steal_time *src = &per_cpu(steal_time, cpu); >> @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) >> } >> PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); >> >> +#else >> + >> +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int);...

...t; push %rdi; >>>>> movslq %edi, %rdi; >>>>> movq __per_cpu_offset(,%rdi,8), %rax; >>>>> cmpb $0, %[offset](%rax); >>>>> setne %al; >>>>> pop %rdi; >>>>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); >>>>> >>>>> And if we could get rid of the sign extend on edi we could avoid all the >>>>> push-pop nonsense, but I'm not sure I see how to do that (then again, >>>>> this asm foo isn't...

On Wed, Feb 15, 2017 at 04:37:50PM -0500, Waiman Long wrote: > +/* > + * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and > + * restoring to/from the stack. It is assumed that the preempted value > + * is at an offset of 16 from the beginning of the kvm_steal_time structure > + * which is verified by the BUILD_BUG_ON() macro below. > + */ > +#define PREEMPTED_OFFSET 16 As per Andrew's suggestion, the 'right' way is something like so. --- asm-offsets_64.c | 11 +++++++++++ kvm.c | 14 ++++---------- 2 files changed, 15...

On Wed, Feb 15, 2017 at 04:37:50PM -0500, Waiman Long wrote: > +/* > + * Hand-optimize version for x86-64 to avoid 8 64-bit register saving and > + * restoring to/from the stack. It is assumed that the preempted value > + * is at an offset of 16 from the beginning of the kvm_steal_time structure > + * which is verified by the BUILD_BUG_ON() macro below. > + */ > +#define PREEMPTED_OFFSET 16 As per Andrew's suggestion, the 'right' way is something like so. --- asm-offsets_64.c | 11 +++++++++++ kvm.c | 14 ++++---------- 2 files changed, 15...