Re: [PATCH 3/7] dma-buf: add dma_fence_chain_alloc/free self tests

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jun 10, 2021 at 11:17:56AM +0200, Christian König wrote:
> Exercise the newly added functions.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

I have honestly no idea what this checks. Spawning a few threads to
validate kmalloc/kfree feels a bit silly. Now testing whether we correctly
rcu-delay the freeing here would make some sense, but even that feels a
bit silly.

I guess if you want this explain with comments what it does and why?
-Daniel


> ---
>  drivers/dma-buf/st-dma-fence-chain.c | 48 ++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
> 
> diff --git a/drivers/dma-buf/st-dma-fence-chain.c b/drivers/dma-buf/st-dma-fence-chain.c
> index 8ce1ea59d31b..855c129c6093 100644
> --- a/drivers/dma-buf/st-dma-fence-chain.c
> +++ b/drivers/dma-buf/st-dma-fence-chain.c
> @@ -95,6 +95,53 @@ static int sanitycheck(void *arg)
>  	return err;
>  }
>  
> +static int __alloc_free(void *arg)
> +{
> +	atomic_t *counter = arg;
> +	int i, j;
> +
> +	for (i = 0; i < 1024; ++i) {
> +		struct dma_fence_chain *chains[64];
> +
> +		for (j = 0; j < ARRAY_SIZE(chains); ++j)
> +			chains[j] = dma_fence_chain_alloc();
> +
> +		for (j = 0; j < ARRAY_SIZE(chains); ++j)
> +			dma_fence_chain_free(chains[j]);
> +
> +		atomic_add(ARRAY_SIZE(chains), counter);
> +	}
> +	return 0;
> +}
> +
> +static int alloc_free(void *arg)
> +{
> +	struct task_struct *threads[8];
> +	atomic_t counter = ATOMIC_INIT(0);
> +	int i, err = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(threads); i++) {
> +		threads[i] = kthread_run(__alloc_free, &counter, "dmabuf/%d",
> +					 i);
> +		if (IS_ERR(threads[i])) {
> +			err = PTR_ERR(threads[i]);
> +			break;
> +		}
> +	}
> +
> +	while (i--) {
> +		int ret;
> +
> +		ret = kthread_stop(threads[i]);
> +		if (ret && !err)
> +			err = ret;
> +	}
> +
> +	pr_info("Completed %u cycles\n", atomic_read(&counter));
> +
> +	return err;
> +}
> +
>  struct fence_chains {
>  	unsigned int chain_length;
>  	struct dma_fence **fences;
> @@ -677,6 +724,7 @@ int dma_fence_chain(void)
>  {
>  	static const struct subtest tests[] = {
>  		SUBTEST(sanitycheck),
> +		SUBTEST(alloc_free),
>  		SUBTEST(find_seqno),
>  		SUBTEST(find_signaled),
>  		SUBTEST(find_out_of_order),
> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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