Re: [PATCH igt] igt/gem_exec_await: Flush the WCB before attempting to queue more work

From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH igt] igt/gem_exec_await: Flush the WCB before attempting to queue more work
Date: Fri, 22 Dec 2017 17:03:46 +0000	[thread overview]
Message-ID: <bde4e166-7f90-40ea-4345-2b35a5a3d136@linux.intel.com> (raw)
In-Reply-To: <20171221154823.23766-1-chris@chris-wilson.co.uk>

On 21/12/2017 15:48, Chris Wilson wrote:
> Ensure that the terminating write into WC-memory is flushed before we
> might trigger a wait for ring space.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   tests/gem_exec_await.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/tests/gem_exec_await.c b/tests/gem_exec_await.c
> index 9c4467922..28b280ff6 100644
> --- a/tests/gem_exec_await.c
> +++ b/tests/gem_exec_await.c
> @@ -222,6 +222,7 @@ static void wide(int fd, int ring_size, int timeout, unsigned int flags)
>   
>   		for (unsigned e = 0; e < nengine; e++)
>   			exec[e].cmd[0] = MI_BATCH_BUFFER_END;
> +		__sync_synchronize();
>   	}
>   
>   	igt_assert_eq(intel_detect_and_clear_missed_interrupts(fd), 0);
> 

In case someone is reading from the same uneducated situation as I was, 
__sync_synchronize emits an mfence instructions which indeed forces a 
flush of the write combine buffer.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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