[igt-dev] [PATCH igt] lib: Avoid rcu_barrier() for gem_quiescent_gpu()

[Antonio Argenziano]

On 31/01/18 01:35, Chris Wilson wrote:
> Using DROP_FREED invokes an rcu_barrier() to ensure that all RCU
> protected objects are freed before it returns. rcu_barrier() is a very
> high latency operation (~50ms at best) which is only required under
> specific circumstances such as when we need a stable object count. By

Do we expect those specific circumstances to be of interest in our 
testing? Or better, do we need a gem_quiescent_gpu that waits on all RCU 
protected objects?

> removing it from gem_quiescent_gpu() we can save over 10s across a BAT
> run.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   lib/drmtest.c     |  3 +--
>   lib/igt_debugfs.c | 14 ++++++++------
>   lib/intel_os.c    | 15 +++++++++------
>   3 files changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/drmtest.c b/lib/drmtest.c
> index fd11f5f58..40bd6fec8 100644
> --- a/lib/drmtest.c
> +++ b/lib/drmtest.c
> @@ -163,8 +163,7 @@ void gem_quiescent_gpu(int fd)
>   {
>   	igt_terminate_spin_batches();
>   
> -	igt_drop_caches_set(fd,
> -			    DROP_ACTIVE | DROP_RETIRE | DROP_IDLE | DROP_FREED);
> +	igt_drop_caches_set(fd, DROP_ACTIVE | DROP_RETIRE | DROP_IDLE);
>   }
>   
>   /**
> diff --git a/lib/igt_debugfs.c b/lib/igt_debugfs.c
> index 1aec079c5..6d9d27d9c 100644
> --- a/lib/igt_debugfs.c
> +++ b/lib/igt_debugfs.c
> @@ -977,13 +977,15 @@ static int get_object_count(int fd)
>    */
>   int igt_get_stable_obj_count(int driver)
>   {
> -	int obj_count;
> -	gem_quiescent_gpu(driver);
> -	obj_count = get_object_count(driver);
> -	/* The test relies on the system being in the same state before and
> +	/*
> +	 * The test relies on the system being in the same state before and
>   	 * after the test so any difference in the object count is a result of
> -	 * leaks during the test. */
> -	return obj_count;
> +	 * leaks during the test.
> +	 * */
> +	igt_drop_caches_set(driver,
> +			    DROP_ACTIVE | DROP_RETIRE | DROP_IDLE | DROP_FREED);
> +
> +	return get_object_count(driver);
>   }
>

Split the next bit in a separate commit?

Thanks,
Antonio

>   void igt_debugfs_dump(int device, const char *filename)
> diff --git a/lib/intel_os.c b/lib/intel_os.c
> index bb2c16bf3..b5d9888d8 100644
> --- a/lib/intel_os.c
> +++ b/lib/intel_os.c
> @@ -96,11 +96,6 @@ intel_get_avail_ram_mb(void)
>   
>   #ifdef HAVE_STRUCT_SYSINFO_TOTALRAM /* Linux */
>   	struct sysinfo sysinf;
> -	int fd;
> -
> -	fd = drm_open_driver(DRIVER_INTEL);
> -	intel_purge_vm_caches(fd);
> -	close(fd);
>   
>   	igt_assert(sysinfo(&sysinf) == 0);
>   	retval = sysinf.freeram;
> @@ -281,6 +276,12 @@ void intel_require_memory(uint64_t count, uint64_t size, unsigned mode)
>   {
>   	uint64_t required, total;
>   
> +	if (!__intel_check_memory(count, size, mode, &required, &total)) {
> +		int fd = drm_open_driver(DRIVER_INTEL);
> +		intel_purge_vm_caches(fd);
> +		close(fd);
> +	}
> +
>   	igt_require_f(__intel_check_memory(count, size, mode,
>   					    &required, &total),
>   		      "Estimated that we need %'llu objects and %'llu MiB for the test, but only have %'llu MiB available (%s%s) and a maximum of %'llu objects\n",
> @@ -298,7 +299,9 @@ void intel_purge_vm_caches(int drm_fd)
>   {
>   	int fd;
>   
> -	igt_drop_caches_set(drm_fd, DROP_SHRINK_ALL | DROP_IDLE | DROP_FREED);
> +	igt_drop_caches_set(drm_fd,
> +			    DROP_ACTIVE | DROP_RETIRE | DROP_IDLE |
> +			    DROP_SHRINK_ALL | DROP_FREED);
>   
>   	fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
>   	if (fd >= 0) {
>