Re: [PATCH kvm-unit-test 6/6] Add a test for kvm-clock

From: Glauber Costa <glommer@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: mtosatti@redhat.com, avi@redhat.com, kvm@vger.kernel.org
Subject: Re: [PATCH kvm-unit-test 6/6] Add a test for kvm-clock
Date: Fri, 27 Aug 2010 08:34:56 -0300	[thread overview]
Message-ID: <20100827113456.GM2985@mothafucka.localdomain> (raw)
In-Reply-To: <20100827054953.7409.25948.stgit@FreeLancer>

On Fri, Aug 27, 2010 at 01:49:53PM +0800, Jason Wang wrote:
> This patch implements two tests for kvmclock. First one check whether
> the date of time returned by kvmclock matches the value got from
> host. Second one check whether the cycle of kvmclock grows
> monotonically in smp guest.
> 
> Three parameters were accepted by the test: test loops, seconds
> since 1970-01-01 00:00:00 UTC which could be easily get through date
> +%s and the max accepted offset value between the tod of guest and
> host.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  config-x86-common.mak |    6 ++
>  x86/README            |    2 +
>  x86/kvmclock_test.c   |  145 +++++++++++++++++++++++++++++++++++++++++++++++++
>  x86/unittests.cfg     |    5 ++
>  4 files changed, 157 insertions(+), 1 deletions(-)
>  create mode 100644 x86/kvmclock_test.c
> 
> diff --git a/config-x86-common.mak b/config-x86-common.mak
> index b8ca859..b541c1c 100644
> --- a/config-x86-common.mak
> +++ b/config-x86-common.mak
> @@ -26,7 +26,8 @@ FLATLIBS = lib/libcflat.a $(libgcc)
>  tests-common = $(TEST_DIR)/vmexit.flat $(TEST_DIR)/tsc.flat \
>                 $(TEST_DIR)/smptest.flat  $(TEST_DIR)/port80.flat \
>                 $(TEST_DIR)/realmode.flat $(TEST_DIR)/msr.flat \
> -               $(TEST_DIR)/hypercall.flat $(TEST_DIR)/sieve.flat
> +               $(TEST_DIR)/hypercall.flat $(TEST_DIR)/sieve.flat \
> +               $(TEST_DIR)/kvmclock_test.flat
>  
>  tests_and_config = $(TEST_DIR)/*.flat $(TEST_DIR)/unittests.cfg
>  
> @@ -70,6 +71,9 @@ $(TEST_DIR)/rmap_chain.flat: $(cstart.o) $(TEST_DIR)/rmap_chain.o \
>  
>  $(TEST_DIR)/svm.flat: $(cstart.o) $(TEST_DIR)/vm.o
>  
> +$(TEST_DIR)/kvmclock_test.flat: $(cstart.o) $(TEST_DIR)/kvmclock.o \
> +                                $(TEST_DIR)/kvmclock_test.o
> +
>  arch_clean:
>  	$(RM) $(TEST_DIR)/*.o $(TEST_DIR)/*.flat \
>  	$(TEST_DIR)/.*.d $(TEST_DIR)/lib/.*.d $(TEST_DIR)/lib/*.o
> diff --git a/x86/README b/x86/README
> index ab5a2ae..4b90080 100644
> --- a/x86/README
> +++ b/x86/README
> @@ -12,3 +12,5 @@ sieve: heavy memory access with no paging and with paging static and with paging
>  smptest: run smp_id() on every cpu and compares return value to number
>  tsc: write to tsc(0) and write to tsc(100000000000) and read it back
>  vmexit: long loops for each: cpuid, vmcall, mov_from_cr8, mov_to_cr8, inl_pmtimer, ipi, ipi+halt
> +kvmclock_test: monotonic cycle test of kvmclock and a sanity test of
> +wallclock
> diff --git a/x86/kvmclock_test.c b/x86/kvmclock_test.c
> new file mode 100644
> index 0000000..cd80915
> --- /dev/null
> +++ b/x86/kvmclock_test.c
> @@ -0,0 +1,145 @@
> +#include "libcflat.h"
> +#include "smp.h"
> +#include "atomic.h"
> +#include "string.h"
> +#include "kvmclock.h"
> +
> +#define DEFAULT_TEST_LOOPS 100000000L
> +#define DEFAULT_THRESHOLD  60L
> +
> +        printf("Check the stability of raw cycle\n");
> +        pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT
> +                          | PVCLOCK_RAW_CYCLE_BIT);
> +        if (cycle_test(ncpus, loops, &ti[1]))
> +                printf("Raw cycle is not stable\n");
> +        else
> +                printf("Raw cycle is stable\n");
> +
> +        pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
> +        printf("Monotonic cycle test:\n");
> +        nerr += cycle_test(ncpus, loops, &ti[0]);
> +
> +        for (i = 0; i < ncpus; ++i)
> +                on_cpu(i, kvm_clock_clear, (void *)0);
> +
> +        return nerr > 0 ? 1 : 0;

another interesting bit of information is the total time taken by
the first cycle_test, compared to the second (They do the same amount
of loops anyway, so no need for further math). We are all pretty sure
the lack of a stable bit will influence kvm clock performance, but
nobody measured by how much yet (in big, big boxes.)