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kvm/x86 : add coalesced pio support

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Coalesced pio is based on coalesced mmio and can be used for some port
like rtc port, pci-host config port and so on.

Specially in case of rtc as coalesced pio, some versions of windows guest
access rtc frequently because of rtc as system tick. guest access rtc like
this: write register index to 0x70, then write or read data from 0x71.
writing 0x70 port is just as index and do nothing else. So we can use
coalesced pio to handle this scene to reduce VM-EXIT time.

When starting and closing a virtual machine, it will access pci-host config
port frequently. So setting these port as coalesced pio can reduce startup
and shutdown time.

without my patch, get the vm-exit time of accessing rtc 0x70 and piix 0xcf8
using perf tools: (guest OS : windows 7 64bit)
IO Port Access  Samples Samples%  Time%  Min Time  Max Time  Avg time
0x70:POUT        86     30.99%    74.59%   9us      29us    10.75us (+- 3.41%)
0xcf8:POUT     1119     2.60%     2.12%   2.79us    56.83us 3.41us (+- 2.23%)

with my patch
IO Port Access  Samples Samples%  Time%   Min Time  Max Time   Avg time
0x70:POUT       106    32.02%    29.47%    0us      10us     1.57us (+- 7.38%)
0xcf8:POUT      1065    1.67%     0.28%   0.41us    65.44us   0.66us (+- 10.55%)

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Peng Hao
2018-10-14 07:09:55 +08:00
committed by Paolo Bonzini
parent 9943450b7b
commit 0804c849f1
4 changed files with 30 additions and 11 deletions
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11
include/uapi/linux/kvm.h
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@@ -420,13 +420,19 @@ struct kvm_run {
struct kvm_coalesced_mmio_zone {
__u64 addr;
__u32 size;
__u32 pad;
union {
__u32 pad;
__u32 pio;
};
};
struct kvm_coalesced_mmio {
__u64 phys_addr;
__u32 len;
__u32 pad;
union {
__u32 pad;
__u32 pio;
};
__u8 data[8];
};
@@ -956,6 +962,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_MSR_PLATFORM_INFO 159
#define KVM_CAP_PPC_NESTED_HV 160
#define KVM_CAP_HYPERV_SEND_IPI 161
#define KVM_CAP_COALESCED_PIO 162
#ifdef KVM_CAP_IRQ_ROUTING