On Thu, Dec 13, 2012 at 01:40:37PM +0100, Paolo Bonzini wrote:
> This patch adds three scenarios to the vmexit test. Two are very simple
> PIO cases that are handled in the kernel (reading from and writing
> to ELCR). The other is an unmapped PIO that is handled in userspace.
>
> The difference between the two reading scenarios is roughly the cost of a
> userspace exit; the existing inl_from_pmtimer test is not precise enough,
> because the device model has a pretty high cost.
>
> The difference between the kernel read and write is the cost of emulation,
> because inl_from_kernel goes through the whole emulation stuff while outl
> does not (it is used for virtio, while the speed of inl matters less).
>
> Example:
>
> vmcall 3898
> inl_from_pmtimer 24615
> inl_from_qemu 20574
> inl_from_kernel 7237
> outl_to_kernel 4451
>
> So the cost of exiting to userspace is 13000 cycles on this machine,
> and the cost of emulation is 3300 cycles.
>
> Suggested-by: Avi Kivity <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
Thanks, applied. On my machine out is faster than vmcall.
vmcall 2681
outl_to_kernel 2358
> ---
> x86/vmexit.c | 30 ++++++++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
>
> diff --git a/x86/vmexit.c b/x86/vmexit.c
> index ad8ab55..98f0ead 100644
> --- a/x86/vmexit.c
> +++ b/x86/vmexit.c
> @@ -4,6 +4,18 @@
> #include "processor.h"
> #include "atomic.h"
>
> +static void outb(unsigned short port, int val)
> +{
> + asm volatile("outb %b0, %w1" : "=a"(val) : "Nd"(port));
> +}
> +
> +static unsigned int inb(unsigned short port)
> +{
> + unsigned int val;
> + asm volatile("xorl %0, %0; inb %w1, %b0" : "=a"(val) : "Nd"(port));
> + return val;
> +}
> +
> static unsigned int inl(unsigned short port)
> {
> unsigned int val;
> @@ -82,6 +94,21 @@ static void inl_pmtimer(void)
> inl(0xb008);
> }
>
> +static void inl_nop_qemu(void)
> +{
> + inl(0x1234);
> +}
> +
> +static void inl_nop_kernel(void)
> +{
> + inb(0x4d0);
> +}
> +
> +static void outl_elcr_kernel(void)
> +{
> + outb(0x4d0, 0);
> +}
> +
> static void ple_round_robin(void)
> {
> struct counter {
> @@ -116,6 +143,9 @@ static struct test {
> { mov_to_cr8, "mov_to_cr8" , .parallel = 1, },
> #endif
> { inl_pmtimer, "inl_from_pmtimer", .parallel = 1, },
> + { inl_nop_qemu, "inl_from_qemu", .parallel = 1 },
> + { inl_nop_kernel, "inl_from_kernel", .parallel = 1 },
> + { outl_elcr_kernel, "outl_to_kernel", .parallel = 1 },
> { ipi, "ipi", is_smp, .parallel = 0, },
> { ipi_halt, "ipi+halt", is_smp, .parallel = 0, },
> { ple_round_robin, "ple-round-robin", .parallel = 1 },
> --
> 1.8.0.2
--
Gleb.
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