On 18/07/18 00:25, Maxym Dmytrychenko wrote:
> On Wed, Jul 18, 2018 at 12:48 AM Mark Thompson <[email protected]> wrote:
>
>> On 17/07/18 17:07, Maxym Dmytrychenko wrote:
>>> Not used VPP sessions, like for hwupload/hwdownload handling,
>>> can increase CPU utilization and this patch fixes it.
>>> thank you,Joe, for the contribution.
>>>
>>> Signed-off-by: Maxym Dmytrychenko <[email protected]>
>>> ---
>>> libavutil/hwcontext_qsv.c | 38 +++++++++++++++++++++++++++++---------
>>> 1 file changed, 29 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/libavutil/hwcontext_qsv.c b/libavutil/hwcontext_qsv.c
>>> index b3eb4a3ea..390c3aac4 100644
>>> --- a/libavutil/hwcontext_qsv.c
>>> +++ b/libavutil/hwcontext_qsv.c
>>> @@ -18,6 +18,7 @@
>>>
>>> #include <stdint.h>
>>> #include <string.h>
>>> +#include <stdatomic.h>
>>>
>>> #include <mfx/mfxvideo.h>
>>>
>>> @@ -56,7 +57,9 @@ typedef struct QSVDeviceContext {
>>>
>>> typedef struct QSVFramesContext {
>>> mfxSession session_download;
>>> + atomic_int session_download_init;
>>> mfxSession session_upload;
>>> + atomic_int session_upload_init;
>>>
>>> AVBufferRef *child_frames_ref;
>>> mfxFrameSurface1 *surfaces_internal;
>>> @@ -146,13 +149,15 @@ static void qsv_frames_uninit(AVHWFramesContext
>> *ctx)
>>> MFXVideoVPP_Close(s->session_download);
>>> MFXClose(s->session_download);
>>> }
>>> - s->session_download = NULL;
>>> + s->session_download = NULL;
>>> + s->session_download_init = 0;
>>>
>>> if (s->session_upload) {
>>> MFXVideoVPP_Close(s->session_upload);
>>> MFXClose(s->session_upload);
>>> }
>>> - s->session_upload = NULL;
>>> + s->session_upload = NULL;
>>> + s->session_upload_init = 0;
>>>
>>> av_freep(&s->mem_ids);
>>> av_freep(&s->surface_ptrs);
>>> @@ -535,13 +540,10 @@ static int qsv_frames_init(AVHWFramesContext *ctx)
>>> s->mem_ids[i] = frames_hwctx->surfaces[i].Data.MemId;
>>> }
>>>
>>> - ret = qsv_init_internal_session(ctx, &s->session_download, 0);
>>> - if (ret < 0)
>>> - return ret;
>>> -
>>> - ret = qsv_init_internal_session(ctx, &s->session_upload, 1);
>>> - if (ret < 0)
>>> - return ret;
>>> + s->session_download = NULL;
>>> + s->session_upload = NULL;
>>> + s->session_download_init = 0;
>>> + s->session_upload_init = 0;
>>>
>>> return 0;
>>> }
>>> @@ -741,6 +743,15 @@ static int qsv_transfer_data_from(AVHWFramesContext
>> *ctx, AVFrame *dst,
>>> mfxSyncPoint sync = NULL;
>>> mfxStatus err;
>>>
>>> + while (!s->session_download_init && !s->session_download) {
>>> + if (atomic_fetch_add(&s->session_download_init, 1) == 0) {
>>> + qsv_init_internal_session(ctx, &s->session_download, 0);
>>> + }
>>> + else {
>>> + av_usleep(1);
>>
>> This races - consider what happens if the other thread is preempted for
>> more than 1µs, or if the initialisation itself takes more than that long.
(Apologies, I misread that the first time - with the spin loop it should only
be a benign race on session_download, but it's still undefined behaviour by C11
and things like tsan will complain about it: read in the non-initialising
thread against write in the initialising thread, after the flag has been set to
1.)
>>
>> You need to actually do some synchronisation here (e.g. with a 'once'
>> variable) - with only atomic flags there is no way to guarantee that the
>> other thread has finished unless you spin, which isn't acceptable.
>>
>> pthread_once was considered but we need to pass s->session_download
> adding mutex - can be overkill for each call of qsv_transfer_data_*
>
> what do you mean by 'once' variable?
> dont really see it currently implemented somewhere...
See AVOnce. It's used in a few places in this role, for example in
hwcontext_d3d11va.c for the library loading.
>>> + }
>>> + }
>>> +
>>> if (!s->session_download) {
>>> if (s->child_frames_ref)
>>> return qsv_transfer_data_child(ctx, dst, src);
>>> @@ -788,6 +799,15 @@ static int qsv_transfer_data_to(AVHWFramesContext
>> *ctx, AVFrame *dst,
>>> mfxSyncPoint sync = NULL;
>>> mfxStatus err;
>>>
>>> + while (!s->session_upload_init && !s->session_upload) {
>>> + if (atomic_fetch_add(&s->session_upload_init, 1) == 0) {
>>> + qsv_init_internal_session(ctx, &s->session_upload, 1);
>>> + }
>>> + else {
>>> + av_usleep(1);
>>> + }
>>> + }
>>> +
>>> if (!s->session_upload) {
>>> if (s->child_frames_ref)
>>> return qsv_transfer_data_child(ctx, dst, src);
>>>
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