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Wed, 11 Mar 2020 03:07:06 +0000 (UTC) Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by gabe.freedesktop.org (Postfix) with ESMTPS id AB9A16E3F5 for ; Wed, 11 Mar 2020 03:07:05 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Mar 2020 20:07:05 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,539,1574150400"; d="scan'208";a="236272055" Received: from adixit-mobl.amr.corp.intel.com (HELO adixit-arch.intel.com) ([10.254.38.38]) by orsmga008.jf.intel.com with ESMTP; 10 Mar 2020 20:07:04 -0700 Date: Tue, 10 Mar 2020 20:05:43 -0700 Message-ID: <87y2s7wpyw.wl-ashutosh.dixit@intel.com> From: "Dixit, Ashutosh" To: Lionel Landwerlin In-Reply-To: <753314a2-1768-0110-ba20-e2515b8e5a1c@intel.com> References: <20200303221905.25866-1-umesh.nerlige.ramappa@intel.com> <20200303221905.25866-8-umesh.nerlige.ramappa@intel.com> <87v9nku0uu.wl-ashutosh.dixit@intel.com> <87o8tb2vlf.wl-ashutosh.dixit@intel.com> <20200309195141.GA9651@orsosgc001.amr.corp.intel.com> <753314a2-1768-0110-ba20-e2515b8e5a1c@intel.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?ISO-8859-4?Q?Goj=F2?=) APEL/10.8 EasyPG/1.0.0 Emacs/26 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Subject: Re: [Intel-gfx] [PATCH 7/7] drm/i915/perf: add flushing ioctl X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Tue, 10 Mar 2020 13:44:30 -0700, Lionel Landwerlin wrote: > > On 09/03/2020 21:51, Umesh Nerlige Ramappa wrote: > > On Wed, Mar 04, 2020 at 09:56:28PM -0800, Dixit, Ashutosh wrote: > >> On Wed, 04 Mar 2020 00:52:34 -0800, Lionel Landwerlin wrote: > >>> > >>> On 04/03/2020 07:48, Dixit, Ashutosh wrote: > >>> > On Tue, 03 Mar 2020 14:19:05 -0800, Umesh Nerlige Ramappa wrote: > >>> >> From: Lionel Landwerlin > >>> >> > >>> >> With the currently available parameters for the i915-perf stream, > >>> >> there are still situations that are not well covered : > >>> >> > >>> >> If an application opens the stream with polling disable or at very > >>> low > >>> >> frequency and OA interrupt enabled, no data will be available even > >>> >> though somewhere between nothing and half of the OA buffer worth of > >>> >> data might have landed in memory. > >>> >> > >>> >> To solve this issue we have a new flush ioctl on the perf stream > >>> that > >>> >> forces the i915-perf driver to look at the state of the buffer when > >>> >> called and makes any data available through both poll() & read() > >>> type > >>> >> syscalls. > >>> >> > >>> >> v2: Version the ioctl (Joonas) > >>> >> v3: Rebase (Umesh) > >>> >> > >>> >> Signed-off-by: Lionel Landwerlin > >>> >> Signed-off-by: Umesh Nerlige Ramappa > >>> > >>> > [snip] > >>> > > >>> >> +/** > >>> >> + * i915_perf_flush_data - handle `I915_PERF_IOCTL_FLUSH_DATA` ioc= tl > >>> >> + * @stream: An enabled i915 perf stream > >>> >> + * > >>> >> + * The intention is to flush all the data available for reading > >>> from the OA > >>> >> + * buffer > >>> >> + */ > >>> >> +static void i915_perf_flush_data(struct i915_perf_stream *stream) > >>> >> +{ > >>> >> +=A0=A0=A0 stream->pollin =3D oa_buffer_check(stream, true); > >>> >> +} > >>> > Since this function doesn't actually wake up any thread (which anyw= ay > >>> can > >>> > be done by sending a signal to the blocked thread), is the only > >>> purpose of > >>> > this function to update OA buffer head/tail? But in that it is not > >>> clear > >>> > why a separate ioctl should be created for this, can't the read() > >>> call > >>> > itself call oa_buffer_check() to update the OA buffer head/tail? > >>> > > >>> > Again just trying to minimize uapi changes if possible. > >>> > >>> Most applications will call read() after being notified by > >>> poll()/select() > >>> that some data is available. > >> > >> Correct this is the standard non blocking read behavior. > >> > >>> Changing that behavior will break some of the existing perf tests . > >> > >> I am not suggesting changing that (that standard non blocking read > >> behavior). > >> > >>> If any data is available, this new ioctl will wake up existing waiters > >>> on > >>> poll()/select(). > >> > >> The issue is we are not calling wake_up() in the above function to wake > >> up > >> any blocked waiters. The ioctl will just update the OA buffer head/tail > >> so > >> that (a) a subsequent blocking read will not block, or (b) a subsequent > >> non > >> blocking read will return valid data (not -EAGAIN), or (c) a poll/sele= ct > >> will not block but return immediately saying data is available. > >> > >> That is why it seems to me the ioctl is not required, updating the OA > >> buffer head/tail can be done as part of the read() (and the poll/selec= t) > >> calls themselves. > >> > >> We will investigate if this can be done and update the patches in the > >> next > >> revision accordingly. Thanks! > > > > In this case, where we are trying to determine if there is any data in > > the oa buffer before the next interrupt has fired, user could call poll > > with a reasonable timeout to determine if data is available or not.=A0 = That > > would eliminate the need for the flush ioctl. Thoughts? > > > > Thanks, > > Umesh > > > I almost forgot why this would cause problem. > > Checking the state of the buffer every time you call poll() will pretty > much guarantee you have at least one report to read every time. > > So that would lead to lot more wakeups :( > > The whole system has to stay "unidirectional" with either interrupts or > timeout driving the wakeups. > > This additional ioctl is the only solution I could find to add one more > input to the wakeup mechanism. Well, aren't we asking the app to sleep for time T and then call flush (followed by read)? Then we might as well ask them to sleep for time T and call poll? Or we can ask them set the hrtimer to T, skip the sleep and call poll (followed by read)? Aren't these 3 mechanisms equivalent? To me the last option seems to be the cleanest. Thanks! _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx