Re: [Qemu-devel] [kvm-unit-tests PATCH v5 09/11] arm: query /dev/kvm for maximum vcpus

[Andrew Jones <drjones@redhat.com>]

On Fri, Jul 31, 2015 at 04:53:59PM +0100, Alex Bennée wrote:
> From: Alex Bennée <alex@bennee.com>
> 
> The previous $(getconf _NPROCESSORS_CONF) isn't correct as the default
> maximum VCPU configuration is 4 on arm64 machines which typically have
> more actual cores.

The kernel should probably bump that up to 8, but that's an aside,
as it wouldn't resolve the general issue.

For this patch, I don't think we need a C utility as we can probe
with QEMU, and thus just need a script.

  $QEMU -machine virt,accel=kvm -smp 9
  Number of SMP cpus requested (9), exceeds max cpus supported by machine `virt' (8)

The script can live in $root/scripts/, which is a directory recently
created for standalone test support.

Thanks,
drew

> 
> This introduces a simple utility program to query the KVM capabilities
> and use the correct maximum number of vcpus.
> 
> [FOR DISCUSSION: this fails on TCG which could use _NPROCESSORS_CONF]
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  arm/unittests.cfg            | 10 +++++-----
>  arm/utils/kvm-query.c        | 41 +++++++++++++++++++++++++++++++++++++++++
>  config/config-arm-common.mak |  8 +++++++-
>  3 files changed, 53 insertions(+), 6 deletions(-)
>  create mode 100644 arm/utils/kvm-query.c
> 
> diff --git a/arm/unittests.cfg b/arm/unittests.cfg
> index 19d72ad..7a3a32b 100644
> --- a/arm/unittests.cfg
> +++ b/arm/unittests.cfg
> @@ -32,30 +32,30 @@ groups = selftest
>  # Test SMP support
>  [selftest::smp]
>  file = selftest.flat
> -smp = $(getconf _NPROCESSORS_CONF)
> +smp = $(./arm/utils/kvm-query max_vcpu)
>  extra_params = -append 'smp'
>  groups = selftest
>  
>  # TLB Torture Tests
>  [tlbflush::all_other]
>  file = tlbflush-test.flat
> -smp = $(getconf _NPROCESSORS_CONF)
> +smp = $(./arm/utils/kvm-query max_vcpu)
>  groups = tlbflush
>  
>  [tlbflush::page_other]
>  file = tlbflush-test.flat
> -smp = $(getconf _NPROCESSORS_CONF)
> +smp = $(./arm/utils/kvm-query max_vcpu)
>  extra_params = -append 'page'
>  groups = tlbflush
>  
>  [tlbflush::all_self]
>  file = tlbflush-test.flat
> -smp = $(getconf _NPROCESSORS_CONF)
> +smp = $(./arm/utils/kvm-query max_vcpu)
>  extra_params = -append 'self'
>  groups = tlbflush
>  
>  [tlbflush::page_self]
>  file = tlbflush-test.flat
> -smp = $(getconf _NPROCESSORS_CONF)
> +smp = $(./arm/utils/kvm-query max_vcpu)
>  extra_params = -append 'page self'
>  groups = tlbflush
> diff --git a/arm/utils/kvm-query.c b/arm/utils/kvm-query.c
> new file mode 100644
> index 0000000..4f979b1
> --- /dev/null
> +++ b/arm/utils/kvm-query.c
> @@ -0,0 +1,41 @@
> +/*
> + * kvm-query.c
> + *
> + * A simple utility to query KVM capabilities.
> + */
> +
> +#include <sys/ioctl.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +
> +#include <string.h>
> +#include <stdio.h>
> +
> +#include <linux/kvm.h>
> +
> +int get_max_vcpu(void)
> +{
> +	int fd = open("/dev/kvm", O_RDWR);
> +	if (fd>0) {
> +		int ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS);
> +		printf("%d\n", ret > 0 ? ret : 0);
> +		close(fd);
> +		return 0;
> +	} else {
> +		return -1;
> +	}
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	for (int i=0; i<argc; i++) {
> +		char *arg = argv[i];
> +		if (strcmp(arg, "max_vcpu") == 0) {
> +			return get_max_vcpu();
> +		}
> +	}
> +
> +	return  -1;
> +}
> diff --git a/config/config-arm-common.mak b/config/config-arm-common.mak
> index 164199b..9c7607b 100644
> --- a/config/config-arm-common.mak
> +++ b/config/config-arm-common.mak
> @@ -13,7 +13,9 @@ tests-common = $(TEST_DIR)/selftest.flat
>  tests-common += $(TEST_DIR)/spinlock-test.flat
>  tests-common += $(TEST_DIR)/tlbflush-test.flat
>  
> -all: test_cases
> +utils-common = $(TEST_DIR)/utils/kvm-query
> +
> +all: test_cases utils
>  
>  ##################################################################
>  phys_base = $(LOADADDR)
> @@ -58,6 +60,9 @@ FLATLIBS = $(libcflat) $(LIBFDT_archive) $(libgcc) $(libeabi)
>  $(libeabi): $(eabiobjs)
>  	$(AR) rcs $@ $^
>  
> +$(TEST_DIR)/utils/%: $(TEST_DIR)/utils/%.c
> +	$(CC) -std=gnu99 -o $@ $^
> +
>  arm_clean: libfdt_clean asm_offsets_clean
>  	$(RM) $(TEST_DIR)/*.{o,flat,elf} $(libeabi) $(eabiobjs) \
>  	      $(TEST_DIR)/.*.d lib/arm/.*.d
> @@ -69,6 +74,7 @@ tests_and_config = $(TEST_DIR)/*.flat $(TEST_DIR)/unittests.cfg
>  generated_files = $(asm-offsets)
>  
>  test_cases: $(generated_files) $(tests-common) $(tests)
> +utils: $(utils-common)
>  
>  $(TEST_DIR)/selftest.elf: $(cstart.o) $(TEST_DIR)/selftest.o
>  $(TEST_DIR)/spinlock-test.elf: $(cstart.o) $(TEST_DIR)/spinlock-test.o
> -- 
> 2.5.0
> 
>