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Hi Andrey,<br>
<br>
<div class="moz-cite-prefix">Am 07.04.21 um 21:44 schrieb Andrey
Grodzovsky:<br>
</div>
<blockquote type="cite" cite="mid:1e4b766d-b5c2-e6b5-8be6-9b2fae3abc94@amd.com">
<p><br>
</p>
<div class="moz-cite-prefix">On 2021-04-07 6:28 a.m., Christian
König wrote:<br>
</div>
<blockquote type="cite" cite="mid:e37bdceb-cdb2-a826-21cf-8cb88748be08@gmail.com"> Hi
Andrey,<br>
<br>
<div class="moz-cite-prefix">Am 06.04.21 um 23:22 schrieb Andrey
Grodzovsky:<br>
</div>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p>Hey Christian, Denis, see bellow - <br>
</p>
<div class="moz-cite-prefix">On 2021-04-06 6:34 a.m.,
Christian König wrote:<br>
</div>
<blockquote type="cite" cite="mid:51d7873d-cf35-6be5-79c2-024937c67f6a@amd.com"> Hi
Andrey,<br>
<br>
well good question. My job is to watch over the
implementation and design and while I always help I can
adjust anybodies schedule.<br>
<br>
Is the patch to print a warning when the hardware is
accessed without holding the locks merged yet? If not then
that would probably be a good starting point.<br>
</blockquote>
<p><br>
</p>
<p>It's merged into amd-staging-drm-next and since I work on
drm-misc-next I will cherry-pick it into there.<br>
</p>
</blockquote>
<br>
Ok good to know, I haven't tracked that one further.<br>
<br>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p> </p>
<p><br>
</p>
<blockquote type="cite" cite="mid:51d7873d-cf35-6be5-79c2-024937c67f6a@amd.com"> <br>
Then we would need to unify this with the SRCU to make sure
that we have both the reset lock as well as block the
hotplug code from reusing the MMIO space.<br>
</blockquote>
<br>
<p>In my understanding there is a significant difference
between handling of GPU reset and unplug - while GPU reset
use case requires any HW accessing code to block and wait
for the reset to finish and then proceed, hot-unplug<br>
is permanent and hence no need to wait and proceed but
rather abort at once.</p>
</blockquote>
<br>
Yes, absolutely correct.<br>
<br>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p> This why I think that in any place we already check for
device reset we should also add a check for hot-unplug but
the handling would be different<br>
in that for hot-unplug we would abort instead of keep
waiting.</p>
</blockquote>
<br>
Yes, that's the rough picture in my head as well.<br>
<br>
Essentially Daniels patch of having an
amdgpu_device_hwaccess_begin()/_end() was the right approach.
You just can't do it in the top level IOCTL handler, but rather
need it somewhere between front end and backend.<br>
</blockquote>
<p><br>
</p>
<p>Can you point me to what patch was it ? Can't find.</p>
</blockquote>
<br>
What I mean was the approach in patch #3 in this series where he
replaced the down_read/up_read with
amdgpu_read_lock()/amdgpu_read_unlock().<br>
<br>
I would just not call it amdgpu_read_lock()/amdgpu_read_unlock(),
but something more descriptive.<br>
<br>
Regards,<br>
Christian.<br>
<br>
<blockquote type="cite" cite="mid:1e4b766d-b5c2-e6b5-8be6-9b2fae3abc94@amd.com">
<p><br>
</p>
<blockquote type="cite" cite="mid:e37bdceb-cdb2-a826-21cf-8cb88748be08@gmail.com"> <br>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p>Similar to handling device reset for unplug we obviously
also need to stop and block any MMIO accesses once device is
unplugged and, as Daniel Vetter mentioned - we have to do it
before finishing pci_remove (early device fini)<br>
and not later (when last device reference is dropped from
user space) in order to prevent reuse of MMIO space we still
access by other hot plugging devices. As in device reset
case we need to cancel all delay works, stop drm schedule,
complete all unfinished fences(both HW and scheduler
fences). While you stated strong objection to force
signalling scheduler fences from GPU reset, quote: <br>
</p>
<p>"you can't signal the dma_fence waiting. Waiting for a
dma_fence also means you wait for the GPU reset to finish.
When we would signal the dma_fence during the GPU reset then
we would run into memory corruption because the hardware
jobs running after the GPU reset would access memory which
is already freed."<br>
To my understating this is a key difference with hot-unplug,
the device is gone, all those concerns are irrelevant and
hence we can actually force signal scheduler fences (setting
and error to them before) to force completion of any<br>
waiting clients such as possibly IOCTLs or async page flips
e.t.c.<br>
</p>
</blockquote>
<br>
Yes, absolutely correct. That's what I also mentioned to Daniel.
When we are able to nuke the device and any memory access it
might do we can also signal the fences.<br>
<br>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p> </p>
<p>Beyond blocking all delayed works and scheduler threads we
also need to guarantee no IOCTL can access MMIO post device
unplug OR in flight IOCTLs are done before we finish
pci_remove (amdgpu_pci_remove for us).<br>
For this I suggest we do something like what we worked on
with Takashi Iwai the ALSA maintainer recently when he
helped implementing PCI BARs move support for snd_hda_intel.
Take a look at<br>
<a class="moz-txt-link-freetext" href="https://nam11.safelinks.protection.outlook.com/?url=https:%2F%2Fcgit.freedesktop.org%2F~agrodzov%2Flinux%2Fcommit%2F%3Fh%3Dyadro%2Fpcie_hotplug%2Fmovable_bars_v9.1%26id%3Dcbaa324799718e2b828a8c7b5b001dd896748497&data=04%7C01%7Candrey.grodzovsky%40amd.com%7Cee01a18abd3b4c85742308d8f9aff67b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637533881445109737%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=TkT2g6JYWW2Pp7RNURfloaksM2%2FAeYgYfxlsQRnPOCo%3D&reserved=0" originalsrc="https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=yadro/pcie_hotplug/movable_bars_v9.1&id=cbaa324799718e2b828a8c7b5b001dd896748497" shash="FHl7248HC/x31wHspNflTb+ftRfxcDYXP2Hw0HqnTdrHWaczzMXdYhA6jSindbHmzza4qGpaEw8rvXJiBkRY3BkuDLhJJ7JSbi4OmUwe/nOT88U5gIkcFiAhGQvVcrmr2Y/j45ubg62EyKL2hYurORVeqj+7ZVDa+P+utpQYQz8=" moz-do-not-send="true">https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=yadro/pcie_hotplug/movable_bars_v9.1&id=cbaa324799718e2b828a8c7b5b001dd896748497</a>
and<br>
<a class="moz-txt-link-freetext" href="https://nam11.safelinks.protection.outlook.com/?url=https:%2F%2Fcgit.freedesktop.org%2F~agrodzov%2Flinux%2Fcommit%2F%3Fh%3Dyadro%2Fpcie_hotplug%2Fmovable_bars_v9.1%26id%3De36365d9ab5bbc30bdc221ab4b3437de34492440&data=04%7C01%7Candrey.grodzovsky%40amd.com%7Cee01a18abd3b4c85742308d8f9aff67b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637533881445119727%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=e%2BuFuY7SEOTngYU%2BnFzW%2BvhEHqdbfliyx%2Fdx%2FhkoIKY%3D&reserved=0" originalsrc="https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=yadro/pcie_hotplug/movable_bars_v9.1&id=e36365d9ab5bbc30bdc221ab4b3437de34492440" shash="uoyaNhinHvE/xWTKNnbny/XoEWda4ENoJEbtErzTv4bEk8x8Dc1J6uMLoBwf6Q4QSevoWQGTQcWJ+AZe/a69lQLeXKNQHz0Ul1t7kZbSEQn91e6a/ULK4Fr4BFwiYdJsxMTFoWRIJpkfGdx7s5/CoH/re504Yue7no8hOpduxpo=" moz-do-not-send="true">https://cgit.freedesktop.org/~agrodzov/linux/commit/?h=yadro/pcie_hotplug/movable_bars_v9.1&id=e36365d9ab5bbc30bdc221ab4b3437de34492440</a><br>
We also had same issue there, how to prevent MMIO accesses
while the BARs are migrating. What was done there is a
refcount was added to count all IOCTLs in flight, for any in
flight IOCTL the BAR migration handler would <br>
block for the refcount to drop to 0 before it would proceed,
for any later IOCTL it stops and wait if device is in
migration state. We even don't need the wait part, nothing
to wait for, we just return with -ENODEV for this case.</p>
</blockquote>
<br>
This is essentially what the DRM SRCU is doing as well.<br>
</blockquote>
<blockquote type="cite" cite="mid:e37bdceb-cdb2-a826-21cf-8cb88748be08@gmail.com"> <br>
For the hotplug case we could do this in the toplevel since we
can signal the fence and don't need to block memory management.<br>
</blockquote>
<p><br>
</p>
<p>To make SRCU 'wait for' all IOCTLs in flight we would need to
wrap every IOCTL ( practically - just drm_ioctl function) with
drm_dev_enter/drm_dev_exit - can we do it ? <br>
</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:e37bdceb-cdb2-a826-21cf-8cb88748be08@gmail.com"> <br>
But I'm not sure, maybe we should handle it the same way as
reset or maybe we should have it at the top level.<br>
</blockquote>
<p><br>
</p>
<p>If by top level you mean checking for device unplugged and
bailing out at the entry to IOCTL or right at start of any
work_item/timer function we have then seems to me it's better
and more clear. Once we flushed all of them in flight there is
no reason for them to execute any more when device is unplugged.<br>
</p>
<p>Andrey<br>
</p>
<p> <br>
</p>
<blockquote type="cite" cite="mid:e37bdceb-cdb2-a826-21cf-8cb88748be08@gmail.com"> <br>
Regards,<br>
Christian.<br>
<br>
<blockquote type="cite" cite="mid:29ffe63b-9049-824f-84fc-a92fdb451e0d@amd.com">
<p>The above approach should allow us to wait for all the
IOCTLs in flight, together with stopping scheduler threads
and cancelling and flushing all in flight work items and
timers i think It should give as full solution for the
hot-unplug case<br>
of preventing any MMIO accesses post device pci_remove.<br>
<br>
Let me know what you think guys.</p>
<p>Andrey</p>
<p><br>
</p>
<blockquote type="cite" cite="mid:51d7873d-cf35-6be5-79c2-024937c67f6a@amd.com"> <br>
And then testing, testing, testing to see if we have missed
something.<br>
<br>
Christian.<br>
<br>
<div class="moz-cite-prefix">Am 05.04.21 um 19:58 schrieb
Andrey Grodzovsky:<br>
</div>
<blockquote type="cite" cite="mid:1e37bb4d-f54d-1b7e-4632-94cfcf749528@amd.com">
<p>Denis, Christian, are there any updates in the plan on
how to move on with this ? As you know I need very
similar code for my up-streaming of device hot-unplug.
My latest solution (<a class="moz-txt-link-freetext" href="https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Farchives%2Famd-gfx%2F2021-January%2F058606.html&data=04%7C01%7Candrey.grodzovsky%40amd.com%7Cee01a18abd3b4c85742308d8f9aff67b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637533881445129722%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=sMISjE%2FOY0KjAY5rOXXy4KoX%2BeKfhROqwNpH0eEbu7k%3D&reserved=0" originalsrc="https://lists.freedesktop.org/archives/amd-gfx/2021-January/058606.html" shash="ZJFWIZXzcZKY5pN5tv3TCwIIGHY9s30XRsxyyPhOBtRC9llxWPUTCUgnV/mo2HWvAAhcyZaTcUeq+K/3UsQitNwkykgRKMT6Gw0obU9KcVf/m2+Q8INspLNAZklpcIzMoaO5qvfUqCFXpaM6e0tBjlq89+ob+YpSDJhtFoqNsPg=" moz-do-not-send="true">https://lists.freedesktop.org/archives/amd-gfx/2021-January/058606.html</a>)
was not acceptable because of low level guards on the
register accessors level which was hurting performance.
Basically I need a way to prevent any MMIO write
accesses from kernel driver after device is removed (UMD
accesses are taken care of by page faulting dummy page).
We are using now hot-unplug code for Freemont program
and so up-streaming became more of a priority then
before. This MMIO access issue is currently my main
blocker from up-streaming. Is there any way I can assist
in pushing this on ?</p>
<p>Andrey <br>
</p>
<div class="moz-cite-prefix">On 2021-03-18 5:51 a.m.,
Christian König wrote:<br>
</div>
<blockquote type="cite" cite="mid:378fdffb-99b5-2a14-736d-a06f310b040c@amd.com">
Am 18.03.21 um 10:30 schrieb Li, Dennis:<br>
<blockquote type="cite" cite="mid:DM5PR12MB253379E8C89D8A20C8A0245AED699@DM5PR12MB2533.namprd12.prod.outlook.com">
<meta name="Generator" content="Microsoft Word 15
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<div class="WordSection1">
<p class="MsoNormal">>>> The GPU reset
doesn't complete the fences we wait for. It only
completes the hardware fences as part of the
reset.<o:p></o:p></p>
<p class="MsoNormal">>>> So waiting for a
fence while holding the reset lock is illegal and
needs to be avoided.<o:p></o:p></p>
<p class="MsoNormal">I understood your concern. It
is more complex for DRM GFX, therefore I abandon
adding lock protection for DRM ioctls now. Maybe
we can try to add all kernel dma_fence waiting in
a list, and signal all in recovery threads. Do you
have same concern for compute cases? </p>
</div>
</blockquote>
<br>
Yes, compute (KFD) is even harder to handle.<br>
<br>
See you can't signal the dma_fence waiting. Waiting for
a dma_fence also means you wait for the GPU reset to
finish.<br>
<br>
When we would signal the dma_fence during the GPU reset
then we would run into memory corruption because the
hardware jobs running after the GPU reset would access
memory which is already freed.<br>
<br>
<blockquote type="cite" cite="mid:DM5PR12MB253379E8C89D8A20C8A0245AED699@DM5PR12MB2533.namprd12.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">>>> Lockdep also
complains about this when it is used correctly.
The only reason it doesn't complain here is
because you use an atomic+wait_event instead of a
locking primitive.<o:p></o:p></p>
<p class="MsoNormal">Agree. This approach will
escape the monitor of lockdep. Its goal is to
block other threads when GPU recovery thread
start. But I couldn’t find a better method to
solve this problem. Do you have some suggestion? </p>
</div>
</blockquote>
<br>
Well, completely abandon those change here.<br>
<br>
What we need to do is to identify where hardware access
happens and then insert taking the read side of the GPU
reset lock so that we don't wait for a dma_fence or
allocate memory, but still protect the hardware from
concurrent access and reset.<br>
<br>
Regards,<br>
Christian.<br>
<br>
<blockquote type="cite" cite="mid:DM5PR12MB253379E8C89D8A20C8A0245AED699@DM5PR12MB2533.namprd12.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best Regards<o:p></o:p></p>
<p class="MsoNormal">Dennis Li<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Koenig,
Christian <a class="moz-txt-link-rfc2396E" href="mailto:Christian.Koenig@amd.com" moz-do-not-send="true"><Christian.Koenig@amd.com></a>
<br>
<b>Sent:</b> Thursday, March 18, 2021 4:59 PM<br>
<b>To:</b> Li, Dennis <a class="moz-txt-link-rfc2396E" href="mailto:Dennis.Li@amd.com" moz-do-not-send="true"><Dennis.Li@amd.com></a>;
<a class="moz-txt-link-abbreviated" href="mailto:amd-gfx@lists.freedesktop.org" moz-do-not-send="true">amd-gfx@lists.freedesktop.org</a>;
Deucher, Alexander <a class="moz-txt-link-rfc2396E" href="mailto:Alexander.Deucher@amd.com" moz-do-not-send="true"><Alexander.Deucher@amd.com></a>;
Kuehling, Felix <a class="moz-txt-link-rfc2396E" href="mailto:Felix.Kuehling@amd.com" moz-do-not-send="true"><Felix.Kuehling@amd.com></a>;
Zhang, Hawking <a class="moz-txt-link-rfc2396E" href="mailto:Hawking.Zhang@amd.com" moz-do-not-send="true"><Hawking.Zhang@amd.com></a><br>
<b>Subject:</b> AW: [PATCH 0/4] Refine GPU
recovery sequence to enhance its stability<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">Exactly
that's what you don't seem to understand.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">The GPU reset
doesn't complete the fences we wait for. It
only completes the hardware fences as part of
the reset.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">So waiting
for a fence while holding the reset lock is
illegal and needs to be avoided.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">Lockdep also
complains about this when it is used
correctly. The only reason it doesn't complain
here is because you use an atomic+wait_event
instead of a locking primitive.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">Regards,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe
UI",sans-serif;color:black">Christian.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div class="MsoNormal" style="text-align:center" align="center">
<hr width="98%" size="2" align="center"> </div>
<div id="divRplyFwdMsg">
<p class="MsoNormal"><b><span style="color:black">Von:</span></b><span style="color:black"> Li, Dennis <<a href="mailto:Dennis.Li@amd.com" moz-do-not-send="true">Dennis.Li@amd.com</a>><br>
<b>Gesendet:</b> Donnerstag, 18. März 2021
09:28<br>
<b>An:</b> Koenig, Christian <<a href="mailto:Christian.Koenig@amd.com" moz-do-not-send="true">Christian.Koenig@amd.com</a>>;
<a href="mailto:amd-gfx@lists.freedesktop.org" moz-do-not-send="true">amd-gfx@lists.freedesktop.org</a>
<<a href="mailto:amd-gfx@lists.freedesktop.org" moz-do-not-send="true">amd-gfx@lists.freedesktop.org</a>>;
Deucher, Alexander <<a href="mailto:Alexander.Deucher@amd.com" moz-do-not-send="true">Alexander.Deucher@amd.com</a>>;
Kuehling, Felix <<a href="mailto:Felix.Kuehling@amd.com" moz-do-not-send="true">Felix.Kuehling@amd.com</a>>;
Zhang, Hawking <<a href="mailto:Hawking.Zhang@amd.com" moz-do-not-send="true">Hawking.Zhang@amd.com</a>><br>
<b>Betreff:</b> RE: [PATCH 0/4] Refine GPU
recovery sequence to enhance its stability</span>
<o:p></o:p></p>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
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<div>
<div>
<p class="MsoNormal">>>> Those two
steps need to be exchanged or otherwise it is
possible that new delayed work items etc are
started before the lock is taken.<br>
What about adding check for
adev->in_gpu_reset in work item? If
exchange the two steps, it maybe introduce the
deadlock. For example, the user thread hold
the read lock and waiting for the fence, if
recovery thread try to hold write lock and
then complete fences, in this case, recovery
thread will always be blocked.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
Best Regards<br>
Dennis Li<br>
-----Original Message-----<br>
From: Koenig, Christian <<a href="mailto:Christian.Koenig@amd.com" moz-do-not-send="true">Christian.Koenig@amd.com</a>>
<br>
Sent: Thursday, March 18, 2021 3:54 PM<br>
To: Li, Dennis <<a href="mailto:Dennis.Li@amd.com" moz-do-not-send="true">Dennis.Li@amd.com</a>>;
<a href="mailto:amd-gfx@lists.freedesktop.org" moz-do-not-send="true">
amd-gfx@lists.freedesktop.org</a>; Deucher,
Alexander <<a href="mailto:Alexander.Deucher@amd.com" moz-do-not-send="true">Alexander.Deucher@amd.com</a>>;
Kuehling, Felix <<a href="mailto:Felix.Kuehling@amd.com" moz-do-not-send="true">Felix.Kuehling@amd.com</a>>;
Zhang, Hawking <<a href="mailto:Hawking.Zhang@amd.com" moz-do-not-send="true">Hawking.Zhang@amd.com</a>><br>
Subject: Re: [PATCH 0/4] Refine GPU recovery
sequence to enhance its stability<br>
<br>
Am 18.03.21 um 08:23 schrieb Dennis Li:<br>
> We have defined two variables
in_gpu_reset and reset_sem in adev object. The
atomic type variable in_gpu_reset is used to
avoid recovery thread reenter and make lower
functions return more earlier when recovery
start, but couldn't block recovery thread when
it access hardware. The r/w semaphore
reset_sem is used to solve these
synchronization issues between recovery thread
and other threads.<br>
><br>
> The original solution locked registers'
access in lower functions, which will
introduce following issues:<br>
><br>
> 1) many lower functions are used in both
recovery thread and others. Firstly we must
harvest these functions, it is easy to miss
someones. Secondly these functions need select
which lock (read lock or write lock) will be
used, according to the thread it is running
in. If the thread context isn't considered,
the added lock will easily introduce deadlock.
Besides that, in most time, developer easily
forget to add locks for new functions.<br>
><br>
> 2) performance drop. More lower functions
are more frequently called.<br>
><br>
> 3) easily introduce false positive
lockdep complaint, because write lock has big
range in recovery thread, but low level
functions will hold read lock may be protected
by other locks in other threads.<br>
><br>
> Therefore the new solution will try to
add lock protection for ioctls of kfd. Its
goal is that there are no threads except for
recovery thread or its children (for xgmi) to
access hardware when doing GPU reset and
resume. So refine recovery thread as the
following:<br>
><br>
> Step 0:
atomic_cmpxchg(&adev->in_gpu_reset, 0,
1)<br>
> 1). if failed, it means system had a
recovery thread running, current thread exit
directly;<br>
> 2). if success, enter recovery
thread;<br>
><br>
> Step 1: cancel all delay works, stop drm
schedule, complete all unreceived fences and
so on. It try to stop or pause other threads.<br>
><br>
> Step 2: call
down_write(&adev->reset_sem) to hold
write lock, which will block recovery thread
until other threads release read locks.<br>
<br>
Those two steps need to be exchanged or
otherwise it is possible that new delayed work
items etc are started before the lock is
taken.<br>
<br>
Just to make it clear until this is fixed the
whole patch set is a NAK.<br>
<br>
Regards,<br>
Christian.<br>
<br>
><br>
> Step 3: normally, there is only recovery
threads running to access hardware, it is safe
to do gpu reset now.<br>
><br>
> Step 4: do post gpu reset, such as call
all ips' resume functions;<br>
><br>
> Step 5: atomic set adev->in_gpu_reset
as 0, wake up other threads and release write
lock. Recovery thread exit normally.<br>
><br>
> Other threads call the amdgpu_read_lock
to synchronize with recovery thread. If it
finds that in_gpu_reset is 1, it should
release read lock if it has holden one, and
then blocks itself to wait for recovery
finished event. If thread successfully hold
read lock and in_gpu_reset is 0, it continues.
It will exit normally or be stopped by
recovery thread in step 1.<br>
><br>
> Dennis Li (4):<br>
> drm/amdgpu: remove reset lock from low
level functions<br>
> drm/amdgpu: refine the GPU recovery
sequence<br>
> drm/amdgpu: instead of using
down/up_read directly<br>
> drm/amdkfd: add reset lock protection
for kfd entry functions<br>
><br>
>
drivers/gpu/drm/amd/amdgpu/amdgpu.h
| 6 +<br>
>
drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
| 14 +-<br>
>
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
| 173 +++++++++++++-----<br>
>
.../gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
| 8 -<br>
>
drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c
| 4 +-<br>
>
drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
| 9 +-<br>
>
drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c
| 5 +-<br>
>
drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c
| 5 +-<br>
>
drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
| 172 ++++++++++++++++-<br>
>
drivers/gpu/drm/amd/amdkfd/kfd_priv.h
| 3 +-<br>
>
drivers/gpu/drm/amd/amdkfd/kfd_process.c
| 4 +<br>
>
.../amd/amdkfd/kfd_process_queue_manager.c
| 17 ++<br>
> 12 files changed, 345 insertions(+), 75
deletions(-)<br>
><o:p></o:p></p>
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