From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH v4] drm: do not sleep on vblank while holding a mutex Date: Mon, 31 Oct 2011 23:03:37 +0100 Message-ID: <20111031220337.GA30420@phenom.ffwll.local> References: <1320097578-9011-1-git-send-email-ihadzic@research.bell-labs.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-fx0-f49.google.com (mail-fx0-f49.google.com [209.85.161.49]) by gabe.freedesktop.org (Postfix) with ESMTP id B3D1A9E733 for ; Mon, 31 Oct 2011 15:02:45 -0700 (PDT) Received: by faaf16 with SMTP id f16so8074283faa.36 for ; Mon, 31 Oct 2011 15:02:44 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1320097578-9011-1-git-send-email-ihadzic@research.bell-labs.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: Ilija Hadzic Cc: dri-devel@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org On Mon, Oct 31, 2011 at 05:46:18PM -0400, Ilija Hadzic wrote: > drm_wait_vblank must be DRM_UNLOCKED because otherwise it > will grab the drm_global_mutex and then go to sleep until the vblank > event it is waiting for. That can wreck havoc in the windowing system > because if one process issues this ioctl, it will block all other > processes for the duration of all vblanks between the current and the > one it is waiting for. In some cases it can block the entire windowing > system. > > v2: incorporate comments received from Daniel Vetter and > Michel Daenzer. > > v3/v4: after a lengty discussion with Daniel Vetter, it was concluded > that the only thing not yet protected with locks and atomic > ops is the write to dev->last_vblank_wait. It's only used in a > debug file in proc, and the current code already employs no > correct locking: the proc file only takes dev->struct_mutex, > whereas drm_wait_vblank implicitly took the drm_global_mutex. > Given all this, it's not worth bothering to try to fix > the locks at this time. > > Signed-off-by: Ilija Hadzic Reviewed-by: Daniel Vetter -- Daniel Vetter Mail: daniel@ffwll.ch Mobile: +41 (0)79 365 57 48