linux-kernel - [PATCH V5 3/3] kvm/x86 : add document for coalesced pio

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Date:   Sun, 14 Oct 2018 07:09:57 +0800
From:   Peng Hao <peng.hao2@....com.cn>
To:     pbonzini@...hat.com, rkrcmar@...hat.com, stefanha@...il.com
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Peng Hao <peng.hao2@....com.cn>
Subject: [PATCH V5 3/3]  kvm/x86 : add document for coalesced pio

Signed-off-by: Peng Hao <peng.hao2@....com.cn>
---
 Documentation/virtual/kvm/api.txt | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 9615b9e..d3a0497 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3678,18 +3678,19 @@ the definition of struct kvm_nested_state, see KVM_GET_NESTED_STATE.
 
 4.116 KVM_(UN)REGISTER_COALESCED_MMIO
 
-Capability: KVM_CAP_COALESCED_MMIO
+Capability: KVM_CAP_COALESCED_MMIO (for coalesced mmio)
+	     KVM_CAP_COALESCED_PIO (for coalesced pio)
 Architectures: all
 Type: vm ioctl
 Parameters: struct kvm_coalesced_mmio_zone
 Returns: 0 on success, < 0 on error
 
-Coalesced mmio is a performance optimization that defers hardware
+Coalesced I/O is a performance optimization that defers hardware
 register write emulation so that userspace exits are avoided.  It is
 typically used to reduce the overhead of emulating frequently accessed
 hardware registers.
 
-When a hardware register is configured for coalesced mmio, write accesses
+When a hardware register is configured for coalesced I/O, write accesses
 do not exit to userspace and their value is recorded in a shared coalesced 
 ring in the kernel.
 
@@ -3700,6 +3701,9 @@ will cause the shared coalesced ring to be processed by userspace
 before emulating the current access. That will reduce the first write 
 access to userspace.
 
+Coalesced pio is based on coalesced mmio. There is little difference between
+coalesced mmio and pio except that coalesced pio is used for ioport.
+
 5. The kvm_run structure
 ------------------------
 
-- 
1.8.3.1