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<div class="moz-cite-prefix">Am 08.04.21 um 10:22 schrieb Christian
König:<br>
</div>
<blockquote type="cite"
cite="mid:b67ab565-e4be-0809-7021-cb59fd10464a@amd.com">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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>
</blockquote>
</blockquote>
<br>
Sorry totally missed this question.<br>
<br>
Yes, exactly that. As discussed for the hotplug case we can do this.<br>
<br>
<blockquote type="cite"
cite="mid:b67ab565-e4be-0809-7021-cb59fd10464a@amd.com">
<blockquote type="cite"
cite="mid:1e4b766d-b5c2-e6b5-8be6-9b2fae3abc94@amd.com">
<p> </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>
</blockquote>
</blockquote>
<br>
Well I'm open to both approaches. I just think having
drm_dev_enter/exit on each work item would be more defensive in case
we forgot to cancel/sync one.<br>
<br>
Christian.<br>
<br>
<blockquote type="cite"
cite="mid:b67ab565-e4be-0809-7021-cb59fd10464a@amd.com">
<blockquote type="cite"
cite="mid:1e4b766d-b5c2-e6b5-8be6-9b2fae3abc94@amd.com">
<p> </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">
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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>
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<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>
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<p class="MsoNormal"><o:p> </o:p></p>
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<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>
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<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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