From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH] dma-buf/sync_file: only enable fence signalling during wait Date: Tue, 12 Jul 2016 16:08:44 +0200 Message-ID: <20160712140844.GM23520@phenom.ffwll.local> References: <1467992691-12442-1-git-send-email-gustavo@padovan.org> <183b15e0-3072-6aa2-7d35-002c20752e0e@linux.intel.com> <20160711202713.GC2565@joana> <58ef685f-0308-6828-6e21-ab5fd1302b84@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from mail-wm0-x244.google.com (mail-wm0-x244.google.com [IPv6:2a00:1450:400c:c09::244]) by gabe.freedesktop.org (Postfix) with ESMTPS id C39928910B for ; Tue, 12 Jul 2016 14:08:49 +0000 (UTC) Received: by mail-wm0-x244.google.com with SMTP id o80so2177737wme.0 for ; Tue, 12 Jul 2016 07:08:49 -0700 (PDT) Content-Disposition: inline In-Reply-To: <58ef685f-0308-6828-6e21-ab5fd1302b84@linux.intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Maarten Lankhorst Cc: marcheu@google.com, Daniel Stone , seanpaul@google.com, Daniel Vetter , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, m.chehab@samsung.com, Gustavo Padovan , John Harrison , laurent.pinchart@ideasonboard.com List-Id: dri-devel@lists.freedesktop.org T24gVHVlLCBKdWwgMTIsIDIwMTYgYXQgMTA6NDY6NDVBTSArMDIwMCwgTWFhcnRlbiBMYW5raG9y c3Qgd3JvdGU6Cj4gT3AgMTEtMDctMTYgb20gMjI6Mjcgc2NocmVlZiBHdXN0YXZvIFBhZG92YW46 Cj4gPiAyMDE2LTA3LTEwIE1hYXJ0ZW4gTGFua2hvcnN0IDxtYWFydGVuLmxhbmtob3JzdEBsaW51 eC5pbnRlbC5jb20+Ogo+ID4KPiA+PiBPcCAwOC0wNy0xNiBvbSAxNzo0NCBzY2hyZWVmIEd1c3Rh dm8gUGFkb3ZhbjoKPiA+Pj4gRnJvbTogR3VzdGF2byBQYWRvdmFuIDxndXN0YXZvLnBhZG92YW5A Y29sbGFib3JhLmNvLnVrPgo+ID4+Pgo+ID4+PiBTaWduYWxsaW5nIGRvZXNuJ3QgbmVlZCB0byBi ZSBlbmFibGVkIGF0IHN5bmNfZmlsZSBjcmVhdGlvbiwgaXQgaXMgb25seQo+ID4+PiByZXF1aXJl 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-0400 Date: Tue, 12 Jul 2016 16:08:44 +0200 From: Daniel Vetter To: Maarten Lankhorst Cc: Gustavo Padovan , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Daniel Stone , Daniel Vetter , Rob Clark , Greg Hackmann , John Harrison , laurent.pinchart@ideasonboard.com, seanpaul@google.com, marcheu@google.com, m.chehab@samsung.com, Sumit Semwal , Gustavo Padovan Subject: Re: [PATCH] dma-buf/sync_file: only enable fence signalling during wait Message-ID: <20160712140844.GM23520@phenom.ffwll.local> Mail-Followup-To: Maarten Lankhorst , Gustavo Padovan , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Daniel Stone , Rob Clark , Greg Hackmann , John Harrison , laurent.pinchart@ideasonboard.com, seanpaul@google.com, marcheu@google.com, m.chehab@samsung.com, Sumit Semwal , Gustavo Padovan References: <1467992691-12442-1-git-send-email-gustavo@padovan.org> <183b15e0-3072-6aa2-7d35-002c20752e0e@linux.intel.com> <20160711202713.GC2565@joana> <58ef685f-0308-6828-6e21-ab5fd1302b84@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <58ef685f-0308-6828-6e21-ab5fd1302b84@linux.intel.com> X-Operating-System: Linux phenom 4.6.0-rc5+ User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 12, 2016 at 10:46:45AM +0200, Maarten Lankhorst wrote: > Op 11-07-16 om 22:27 schreef Gustavo Padovan: > > 2016-07-10 Maarten Lankhorst : > > > >> Op 08-07-16 om 17:44 schreef Gustavo Padovan: > >>> From: Gustavo Padovan > >>> > >>> Signalling doesn't need to be enabled at sync_file creation, it is only > >>> required if userspace waiting the fence to signal through poll(). > >>> > >>> Thus we delay fence_add_callback() until poll is called. It only adds the > >>> callback the first time poll() is called. This avoid re-adding the same > >>> callback multiple times. > >>> > >>> v2: rebase and update to work with new fence support for sync_file > >>> > >>> Signed-off-by: Gustavo Padovan > >>> --- > >>> This patch applies on top of my latest sync_file changes to support > >>> fence_array: https://lkml.org/lkml/2016/7/4/534 > >>> > >>> drivers/dma-buf/sync_file.c | 23 ++++++++++++++--------- > >>> include/linux/sync_file.h | 2 ++ > >>> 2 files changed, 16 insertions(+), 9 deletions(-) > >>> > >>> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c > >>> index 61a687c..1db4a64 100644 > >>> --- a/drivers/dma-buf/sync_file.c > >>> +++ b/drivers/dma-buf/sync_file.c > >>> @@ -86,8 +86,6 @@ struct sync_file *sync_file_create(struct fence *fence) > >>> fence->ops->get_timeline_name(fence), fence->context, > >>> fence->seqno); > >>> > >>> - fence_add_callback(fence, &sync_file->cb, fence_check_cb_func); > >>> - > >>> return sync_file; > >>> } > >>> EXPORT_SYMBOL(sync_file_create); > >>> @@ -269,9 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a, > >>> goto err; > >>> } > >>> > >>> - fence_add_callback(sync_file->fence, &sync_file->cb, > >>> - fence_check_cb_func); > >>> - > >>> strlcpy(sync_file->name, name, sizeof(sync_file->name)); > >>> return sync_file; > >>> > >>> @@ -286,7 +281,6 @@ static void sync_file_free(struct kref *kref) > >>> struct sync_file *sync_file = container_of(kref, struct sync_file, > >>> kref); > >>> > >>> - fence_remove_callback(sync_file->fence, &sync_file->cb); > >>> fence_put(sync_file->fence); > >>> kfree(sync_file); > >>> } > >>> @@ -306,13 +300,24 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait) > >>> > >>> poll_wait(file, &sync_file->wq, wait); > >>> > >>> + if (!sync_file->enabled) { > >>> + fence_add_callback(sync_file->fence, &sync_file->cb, > >>> + fence_check_cb_func); > >>> + sync_file->enabled = true; > >>> + } > >> Won't this blow up completely with 2 threads polling at the same time? > > Indeed, using atomic operations on enabled should fix this. > No, it still would blow up without locking around fence_remove/add_callback too.. > > Personally I would just add the callback once, then remove it in destructor. > > Something like: > > poll: > if (!atomic_xchg(&sync_file->enabled, 1)) { > if (fence_add_callback(...) < 0) > wake up sync_file->wq, fence is signaled > } > > sync_file_free: > if (atomic_read(&sync_file->enabled)) > fence_remove_callback(...); > > fence_put() > > It's not like fence can disable hw signaling when all callbacks are removed anyway, > it's harmless to keep it on the list. +1 from me on this plan, removing the callbacks doesn't provide any value (before the sync_file is destroyed). Also, when someone polls, you can expect to get repolled a lot until the fences finally all signal. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch