Re: [Qemu-devel] [PULL 35/44] block: Use QEMU_CLOCK_VIRTUAL for the accounting code in qtest mode

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/11/2015 15:14, Stefan Hajnoczi wrote:
> From: Alberto Garcia <berto@igalia.com>
> 
> This patch switches to QEMU_CLOCK_VIRTUAL for the accounting code in
> qtest mode, and makes the latency of the operation constant. This way we
> can perform tests on the accounting code with reproducible results.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Message-id: 35ed0501450fa572684e9b5e92c361ab6cce565b.1446044838.git.berto@igalia.com
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/accounting.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/block/accounting.c b/block/accounting.c
> index a941931..05a5c5f 100644
> --- a/block/accounting.c
> +++ b/block/accounting.c
> @@ -25,14 +25,20 @@
>  #include "block/accounting.h"
>  #include "block/block_int.h"
>  #include "qemu/timer.h"
> +#include "sysemu/qtest.h"
>  
>  static QEMUClockType clock_type = QEMU_CLOCK_REALTIME;
> +static const int qtest_latency_ns = NANOSECONDS_PER_SECOND / 1000;
>  
>  void block_acct_init(BlockAcctStats *stats, bool account_invalid,
>                       bool account_failed)
>  {
>      stats->account_invalid = account_invalid;
>      stats->account_failed = account_failed;
> +
> +    if (qtest_enabled()) {
> +        clock_type = QEMU_CLOCK_VIRTUAL;
> +    }
>  }
>  
>  void block_acct_cleanup(BlockAcctStats *stats)
> @@ -84,6 +90,10 @@ void block_acct_done(BlockAcctStats *stats, BlockAcctCookie *cookie)
>      int64_t time_ns = qemu_clock_get_ns(clock_type);
>      int64_t latency_ns = time_ns - cookie->start_time_ns;
>  
> +    if (qtest_enabled()) {
> +        latency_ns = qtest_latency_ns;
> +    }
> +
>      assert(cookie->type < BLOCK_MAX_IOTYPE);
>  
>      stats->nr_bytes[cookie->type] += cookie->bytes;
> @@ -107,6 +117,10 @@ void block_acct_failed(BlockAcctStats *stats, BlockAcctCookie *cookie)
>          int64_t time_ns = qemu_clock_get_ns(clock_type);
>          int64_t latency_ns = time_ns - cookie->start_time_ns;
>  
> +        if (qtest_enabled()) {
> +            latency_ns = qtest_latency_ns;
> +        }
> +
>          stats->total_time_ns[cookie->type] += latency_ns;
>          stats->last_access_time_ns = time_ns;
>  
> 

Using QEMU_CLOCK_VIRTUAL makes sense but for the other part, could the
test instead use the null backend?

Paolo