Re: [Qemu-devel] TCG baremetal tests repo

[Frederic Konrad]

On 22/06/2015 12:54, Alexander Spyridakis wrote:
> Hello all,
>
> You can find the latest tcg atomic test payload in the following repo:
> > git clone https://git.virtualopensystems.com/dev/tcg_baremetal_tests.git
>
> You also need an arm baremetal cross-compiler like arm-none-gnueabi- 
> (arm) and the usual aarch64-linux-gnu- (arm64). Due to a PSCI bug in 
> the current multithreading tcg repo, the atomic test was modified to 
> work also on the vexpress machine model.
>
> To run it:
> > make vexpress (or virt/virt64 for other targets)
> > ../mttcg/arm-softmmu/qemu-system-arm -nographic -M vexpress-a15 
> -kernel build-vexpress/image-vexpress.axf -smp 4
>
> On my machine it takes around 30 seconds for one run of the test and 
> the results vary from as low as 5 to 30 errors per vCPU per 10 million 
> iterations (no errors with KVM). It is also very interesting to note, 
> that the current test finishes faster on upstream qemu than 
> multithreaded qemu.
>
> Best regards.

Hi,

I just tested this with vexpress, seems ATOMIC is not defined by default 
it uses:

void non_atomic_lock(int *lock_var)
{
    while (*lock_var != 0);
    *lock_var = 1;
}

void non_atomic_unlock(int *lock_var)
{
    *lock_var = 0;
}

instead of:

void atomic_lock(int *lock_var)
{
    while (__sync_lock_test_and_set(lock_var, 1));
}

void atomic_unlock(int *lock_var)
{
    __sync_lock_release(lock_var);
}

It doesn't cause any errors upstream but a lot on mttcg and mttcg is 
faster in this
case.

I don't have any error when I use ATOMIC like this:

diff --git a/helpers.h b/helpers.h
index b5810ad..427659f 100644
--- a/helpers.h
+++ b/helpers.h
@@ -36,13 +36,8 @@
 #define SYS_CFGCTR_WRITE   0x40000000
 #define SYS_CFG_SHUTDOWN   0x00800000

-#ifdef ATOMIC
 #define LOCK   atomic_lock
 #define UNLOCK atomic_unlock
-#else
-#define LOCK   non_atomic_lock
-#define UNLOCK non_atomic_unlock
-#endif

 int online_cpus;
 int global_lock;

but it's slower than upstream which I think is normal. We can have two CPUs
fighting for the lock in mttcg but not in upstream as VCPUs doesn't run 
at the same
time.

Fred