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<6ae2d00d-7955-d12b-5b56-955ef72ece26@nvidia.com> <1767e50f-efb7-5e89-22f6-0917821b660d@nvidia.com> <235a4cd4-4d4a-04b8-6c65-43a4dba48a0b@nvidia.com> Message-ID: Date: Sat, 2 May 2020 09:14:19 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <235a4cd4-4d4a-04b8-6c65-43a4dba48a0b@nvidia.com> X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-US DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1588436085; bh=OiDqyr/JazfyrNaV3JMZnmdkFchj7uL7aCaOoPT7eTM=; h=X-PGP-Universal:Subject:From:To:CC:References:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Transfer-Encoding: Content-Language; b=C7tRvf/nmvVHeR91VscQFb04J8zZjd/KVLgtpdsFah0LqQ6hYEKacQFB3u47l91DH LDXEP6EEyl46pGtogiqNGKNZUyl0SbwvHF8winrTC7IlTMC6d9H46twAL4lBW/TwYY VPNgTkQOywPeBBKcSnaUI8sWMBgEetqA5jImPj/s1g2r0XUNg94x01/UPBkfHntfb8 XuLkUW/Mto+5cwp5N2crKhSZea6xq9fV+j6SW9+7q7wDKJEXXDjcdiptHRLK6v8n2F mmDZbgYDSqqfCA1b6oy+m8pRbr93Leh7B4oXrN4/Svgu2Jv3vm1z+c13eT+T5d2GHR Hc5oP/fmbqoRQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/2/20 9:03 AM, Sowjanya Komatineni wrote: > > On 5/2/20 8:38 AM, Sowjanya Komatineni wrote: >> >> On 5/2/20 8:16 AM, Dmitry Osipenko wrote: >>> 02.05.2020 06:55, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> On 5/1/20 8:39 PM, Sowjanya Komatineni wrote: >>>>> >>>>> On 5/1/20 2:05 PM, Sowjanya Komatineni wrote: >>>>>> >>>>>> On 5/1/20 1:58 PM, Sowjanya Komatineni wrote: >>>>>>> >>>>>>> On 5/1/20 1:44 PM, Sowjanya Komatineni wrote: >>>>>>>> >>>>>>>> On 5/1/20 11:03 AM, Sowjanya Komatineni wrote: >>>>>>>>> >>>>>>>>> On 4/30/20 4:33 PM, Sowjanya Komatineni wrote: >>>>>>>>>> >>>>>>>>>> On 4/30/20 4:14 PM, Sowjanya Komatineni wrote: >>>>>>>>>>>>>>>>> And in this case synchronization between start/finish >>>>>>>>>>>>>>>>> threads should be >>>>>>>>>>>>>>>>> needed in regards to freezing. >>>>>>>>>>>>>>>> Was thinking to have counter to track outstanding frame >>>>>>>>>>>>>>>> w.r.t single shot issue b/w start and finish and allow to >>>>>>>>>>>>>>>> freeze only when no outstanding frames in process. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> This will make sure freeze will not happen when any=20 >>>>>>>>>>>>>>>> buffers >>>>>>>>>>>>>>>> are in progress >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Note that this could be a wrong assumption, I'm not >>>>>>>>>>>>>>>>> closely familiar >>>>>>>>>>>>>>>>> with how freezer works. >>>>>>>>>>>>>>> kthread_start can unconditionally allow try_to_freeze=20 >>>>>>>>>>>>>>> before >>>>>>>>>>>>>>> start of frame capture >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> We can compute captures inflight w.r.t single shot issued >>>>>>>>>>>>>>> during capture start and finished frames by kthread_finish >>>>>>>>>>>>>>> and allow kthread_finish to freeze only when captures >>>>>>>>>>>>>>> inflight is 0. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> This allows freeze to happen b/w frames but not in=20 >>>>>>>>>>>>>>> middle of >>>>>>>>>>>>>>> frame >>>>>>>>>>>> will have caps inflight check in v12 to allow freeze finish >>>>>>>>>>>> thread only when no captures are in progress >>>>>>>>>>> >>>>>>>>>>> try_to_freeze() returns thread frozen state and looks like we >>>>>>>>>>> can use this in kthread finish to allow finish thread to freeze >>>>>>>>>>> only when kthread_start is already frozen and no buffers in >>>>>>>>>>> progress/initiated for capture. >>>>>>>>>>> >>>>>>>>>> chan->capture_frozen holds frozen state returned from >>>>>>>>>> try_to_freeze() in start kthread >>>>>>>>>> >>>>>>>>>> chan->capture_reqs increments after every single shot issued. >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> static int chan_capture_kthread_finish(void *data) >>>>>>>>>> >>>>>>>>>> { >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D data; >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_channel_buffer *buf; >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 int caps_inflight; >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 set_freezable(); >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 while (1) { >>>>>>>>>> wait_event_interruptible(chan->done_wait, >>>>>>>>>> =C2=A0!list_empty(&chan->done) || >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 = =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0kthread_should_stop()); >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 /* dequeue buffers a= nd finish capture */ >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 buf =3D dequeue_buf_= done(chan); >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 while (buf) { >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 t= egra_channel_capture_done(chan, buf); >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 b= uf =3D dequeue_buf_done(chan); >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 } >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 if (kthread_should_s= top()) >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 b= reak; >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 caps_inflight =3D ch= an->capture_reqs - chan->sequence; >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 if (chan->capture_fr= ozen && !caps_inflight) >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 t= ry_to_freeze(); >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 } >>>>>>>>>> >>>>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 return 0; >>>>>>>>>> } >>>>>>>>> >>>>>>>>> Freezing happens prior to suspend() during suspend entry and when >>>>>>>>> we implement suspend/resume during suspend we stop streaming=20 >>>>>>>>> where >>>>>>>>> we stop threads anyway. >>>>>>>>> >>>>>>>>> So, was thinking why we need these threads freezable here? >>>>>>>>> >>>>>>>>> >>>>>>>> Hi Dmitry, >>>>>>>> >>>>>>>> Did some testing and below are latest observation and fix I=20 >>>>>>>> tested. >>>>>>>> >>>>>>>> wait_event_interruptible() uses schedule() which blocks the=20 >>>>>>>> freezer. >>>>>>>> When I do suspend while keeping streaming active in background, I >>>>>>>> see freezing of these threads fail and call trace shows __schedule >>>>>>>> -> __switch_to from these kthreads. >>>>>>>> >>>>>>>> wait_event_freezable() uses freezable_schedule() which should not >>>>>>>> block the freezer but we can't use this here as we need=20 >>>>>>>> conditional >>>>>>>> try_to_freeze(). >>>>>>>> >>>>>>>> >>>>>>>> So, doing below sequence works where we set PF_FREEZER_SKIP flag >>>>>>>> thru freezer_not_count() before wait_event which calls schedule() >>>>>>>> and remove PF_FREEZER_SKIP after schedule allows try_to_freeze to >>>>>>>> work and also conditional try_to_freeze below prevents freezing >>>>>>>> thread in middle of capture. >>>>>>>> >>>>>>>> while (1) { >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 freezer_not_count() >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 wait_event_interruptible() >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 freezer_count() >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 ... >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 ... >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 if (chan->capture_frozen && !caps_infligh= t) >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 try_to_freeze() >>>>>>>> } >>>>>>>> >>>>>>>> Please comment if you agree with above sequence. Will include this >>>>>>>> in v12. >>>>>>>> >>>>>> sorry, freezer_count() does try_to_freeze after clearing skip flag. >>>>>> So, dont think we can use this as we need conditional try_to_freeze. >>>>>> Please ignore above sequence. >>>>>>> Or probably we can take closer look on this later when we add >>>>>>> suspend/resume support as it need more testing as well. >>>>>>> >>>>>>> As this is initial series which has TPG only I think we shouldn't >>>>>>> get blocked on this now. Series-2 and 3 will be for sensor support >>>>>>> and on next series when we add suspend/resume will look into this. >>>>>>> >>>>>>> >>>>> When freeze activity starts and in case if finish thread freezes=20 >>>>> prior >>>>> to start thread issuing capture, its the VI hardware writes data to >>>>> the allocated buffer address. >>>>> >>>>> finish thread just checks for the event from the hardware and we=20 >>>>> don't >>>>> handle/process directly on memory in this driver. >>>>> >>>>> So even we freeze done thread when single shot is issued frame buffer >>>>> gets updated. >>>>> >>>>> In case if capture thread is frozen there will not buffers queued to >>>>> process by finish thread. So, this will not be an issue. >>>>> >>>>> So, probably we don't need to do conditional try_to_freeze and=20 >>>>> what we >>>>> have should work good in this corner case. >>>>> >>>> I still need to change wait_event_interruptible() to >>>> wait_event_freezable() but no need to synchronize finish thread freeze >>>> with start thread as even on issuing capture start its vi hardware=20 >>>> that >>>> does frame buffer update and finish thread just checks for mw_ack=20 >>>> event >>>> and returns buffer to application. >>> The problem we are primarily trying to avoid is to have suspending=20 >>> being >>> done in the middle of IO. >>> >>> IIUC, even if system will be suspended in the middle of VI IO, it won't >>> be fatal. In worst case the buffer capture should fail on resume from >>> suspend. Could you please try to simulate this potential issue and see >>> what result will be on suspending in the middle of VI IO? >>> >>> We don't want to suspend system / stop streaming in the middle of=20 >>> IO, so >>> this problem of a proper threads tear-down still exists. It should >>> become easier to resolve the problem in a case of a proper suspending >>> callback because the "start" thread could be turned down at any=20 >>> time, so >>> it should be easier to maintain a proper tear-down order when threads >>> are fully controlled by the driver, i.e. the "start" thread goes down >>> first and the "finish" is second, blocking until the capture is=20 >>> completed. > > I don't see issue of tear-down threads in case of suspend as we do=20 > stop streaming where thread stop happens on both threads and are=20 > stopped only after processing all outstanding buffers. > > Regarding freezing activity during suspend, If done thread freezes=20 > prior to processing buffers for finish, vi hardware is still active by=20 > this time which will update the frame buffer for initiated capture.=20 > Driver is not directly involved in this frame buffer update. > > Finish thread only checks for completion to return buffers back to the=20 > application when done. when done thread freeze happens after start thread initiated capture, vi=20 hardware continues to update frame buffer for ongoing capture till it=20 hits driver suspend callback. Yes worst case this frame data may not be=20 valid data if invoking of this driver suspend happens immediate after=20 this thread freeze during system suspend. But driver will still hold buffers to return which will be returned back=20 on resume when threads are out from frozen state. > > >>> I think yours suggestion about dropping the freezing from the threads >>> for now and returning back to it later on (once a proper suspend/resume >>> support will be added) sounds reasonable. >>> >>> But if you'd want to keep the freezing, then the easy solution could be >>> like that: >>> >>> =C2=A0=C2=A0 1. "start" thread could freeze at any time >>> =C2=A0=C2=A0 2. "finish" thread could freeze only when the "start" thre= ad is=20 >>> frozen >>> and capture isn't in-progress. Use frozen(kthread_start_capture) to >>> check the freezing state. >>> >>> https://elixir.bootlin.com/linux/v5.7-rc3/source/include/linux/freezer.= h#L25=20 >>> >> >> That's exactly what I tried, below is the snippet. >> >> But as mentioned I am seeing freezing fail when I=20 >> wait_event_interruptible() in either of the threads. >> >> =C2=A0=C2=A0 60.368709] Call trace: >> [=C2=A0=C2=A0 60.371216] __switch_to+0xec/0x140 >> [=C2=A0=C2=A0 60.374768] __schedule+0x32c/0x668 >> [=C2=A0=C2=A0 60.378315] schedule+0x78/0x118 >> [=C2=A0=C2=A0 60.381606]=C2=A0 chan_capture_kthread_finish+0x244/0x2a0 [= tegra_video] >> [=C2=A0=C2=A0 60.387865] kthread+0x124/0x150 >> [=C2=A0=C2=A0 60.391150] ret_from_fork+0x10/0x1c >> >> wait_event_interruptible() API uses schedule() which blocks freezer=20 >> while wait_event_freezable APIs uses freezable_schedule() which=20 >> allows to skip freezer during schedule and then clears skip and calls=20 >> try_to_freeze() >> >> But we can't use wait_event_freezable() here as we need conditional=20 >> freeze. >> >> >> =C2=A0=C2=A0=C2=A0 while (1) { >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 caps_inflight =3D chan->capture_re= qs - chan->sequence; >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 if (frozen(chan->kthread_start_cap= ture) && !caps_inflight) >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 wait_event_free= zable(chan->done_wait, >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0 !list_empty(&chan->done) || >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0 kthread_should_stop()); >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 else >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 wait_event_inte= rruptible(chan->done_wait, >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0!list_empty(&chan->done) || >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0kthread_should_stop()); >> >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 /* dequeue buffers and finish capt= ure */ >> >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 ... >> >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 ... >> >> >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 if (kthread_should_stop()) >> =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 break; >> =C2=A0=C2=A0=C2=A0 } >>