Patchwork [v2] powerpc: kvm: optimize "sc 1" as fast return

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Submitter pingfan liu
Date Nov. 15, 2013, 8:35 a.m.
Message ID <1384504501-19348-2-git-send-email-pingfank@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/291506/
State New
Headers show

Comments

pingfan liu - Nov. 15, 2013, 8:35 a.m.
In some scene, e.g openstack CI, PR guest can trigger "sc 1" frequently,
this patch optimizes the path by directly delivering BOOK3S_INTERRUPT_SYSCALL
to HV guest, so powernv can return to HV guest without heavy exit, i.e,
no need to swap TLB, HTAB,.. etc

Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv.c            |  6 ------
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 11 ++++++++++-
 2 files changed, 10 insertions(+), 7 deletions(-)
Paul Mackerras - Nov. 16, 2013, 7 a.m.
On Fri, Nov 15, 2013 at 04:35:01PM +0800, Liu Ping Fan wrote:
>  
> +sc_1_fast_return:
> +	mtspr	SPRN_SRR0,r10
> +	mtspr	SPRN_SRR1,r11
> +	li	r10, BOOK3S_INTERRUPT_SYSCALL
> +	li      r11, (MSR_ME << 1) | 1  /* synthesize MSR_SF | MSR_ME */
> +	rotldi  r11, r11, 63

You need a "mr r4, r9" instruction here, because fast_guest_return
needs the vcpu pointer in r4.  Apart from that this looks fine.

> +	b	fast_guest_return

Paul.
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pingfan liu - Nov. 18, 2013, 1:06 a.m.
On Sat, Nov 16, 2013 at 3:00 PM, Paul Mackerras <paulus@samba.org> wrote:
> On Fri, Nov 15, 2013 at 04:35:01PM +0800, Liu Ping Fan wrote:
>>
>> +sc_1_fast_return:
>> +     mtspr   SPRN_SRR0,r10
>> +     mtspr   SPRN_SRR1,r11
>> +     li      r10, BOOK3S_INTERRUPT_SYSCALL
>> +     li      r11, (MSR_ME << 1) | 1  /* synthesize MSR_SF | MSR_ME */
>> +     rotldi  r11, r11, 63
>
> You need a "mr r4, r9" instruction here, because fast_guest_return
> needs the vcpu pointer in r4.  Apart from that this looks fine.
>
Will fix it.

Thanks and regards,
Pingfan
>> +     b       fast_guest_return
>
> Paul.
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Patch

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 62a2b5a..73dc852 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -628,12 +628,6 @@  static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		/* hcall - punt to userspace */
 		int i;
 
-		if (vcpu->arch.shregs.msr & MSR_PR) {
-			/* sc 1 from userspace - reflect to guest syscall */
-			kvmppc_book3s_queue_irqprio(vcpu, BOOK3S_INTERRUPT_SYSCALL);
-			r = RESUME_GUEST;
-			break;
-		}
 		run->papr_hcall.nr = kvmppc_get_gpr(vcpu, 3);
 		for (i = 0; i < 9; ++i)
 			run->papr_hcall.args[i] = kvmppc_get_gpr(vcpu, 4 + i);
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index c71103b..a463f08 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1388,7 +1388,8 @@  kvmppc_hisi:
 hcall_try_real_mode:
 	ld	r3,VCPU_GPR(R3)(r9)
 	andi.	r0,r11,MSR_PR
-	bne	guest_exit_cont
+	/* sc 1 from userspace - reflect to guest syscall */
+	bne	sc_1_fast_return
 	clrrdi	r3,r3,2
 	cmpldi	r3,hcall_real_table_end - hcall_real_table
 	bge	guest_exit_cont
@@ -1409,6 +1410,14 @@  hcall_try_real_mode:
 	ld	r11,VCPU_MSR(r4)
 	b	fast_guest_return
 
+sc_1_fast_return:
+	mtspr	SPRN_SRR0,r10
+	mtspr	SPRN_SRR1,r11
+	li	r10, BOOK3S_INTERRUPT_SYSCALL
+	li      r11, (MSR_ME << 1) | 1  /* synthesize MSR_SF | MSR_ME */
+	rotldi  r11, r11, 63
+	b	fast_guest_return
+
 	/* We've attempted a real mode hcall, but it's punted it back
 	 * to userspace.  We need to restore some clobbered volatiles
 	 * before resuming the pass-it-to-qemu path */