Re: [RFC 0/5] Discussion around eviction improvements
Am 14.05.24 um 17:14 schrieb Tvrtko Ursulin: On 13/05/2024 14:49, Tvrtko Ursulin wrote: On 09/05/2024 13:40, Tvrtko Ursulin wrote: On 08/05/2024 19:09, Tvrtko Ursulin wrote: From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Since yesterday I also briefly tested with Far Cry New Dawn. One run each so possibly doesn't mean anything apart that there isn't a regression aka migration throttling is keeping things at bay even with increased requests to migrate things back to VRAM: before after min/avg/max fps 36/44/54 37/45/55 Cyberpunk 2077 from yesterday was similarly close: 26.96/29.59/30.40 29.70/30.00/30.32 I guess the real story is proper DGPU where misplaced buffers have a real cost. I found one game which regresses spectacularly badly with this series - Assasin's Creed Valhalla. The built-in benchmark at least. The game appears to have a working set much larger than the other games I tested, around 5GiB total during the benchmark. And for some reason migration throttling totally fails to put it in check. I will be investigating this shortly. I think that the conclusion is everything I attempted to add relating to TTM_PL_PREFERRED does not really work as I initially thought it did. Therefore please imagine this series as only containing patches 1, 2 and 5. Noted (and I had just started to wrap my head around that idea). (And FWIW it was quite annoying to get to the bottom of since for some reason the system exibits some sort of a latching behaviour, where on some boots and/or some minutes of runtime things were fine, and then it would latch onto a mode where the TTM_PL_PREFERRED induced breakage would show. And sometimes this breakage would appear straight away. Odd.) Welcome to my world. You improve one use case and four other get a penalty. Even when you know the code and potential use cases inside out it's really hard to predict how some applications and the core memory management behave sometimes. I still need to test though if the subset of patches manage to achieve some positive improvement on their own. It is possible, as patch 5 marks more buffers for re-validation so once overcommit subsides they would get promoted to preferred placement straight away. And 1&2 are notionally fixes for migration throttling so at least in broad sense should be still valid as discussion points. Yeah, especially 5 kind of makes sense but could potentially lead to higher overhead. Need to see how we can better handle that. Regards, Christian. Regards, Tvrtko Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check a
Re: [RFC 0/5] Discussion around eviction improvements
On 13/05/2024 14:49, Tvrtko Ursulin wrote: On 09/05/2024 13:40, Tvrtko Ursulin wrote: On 08/05/2024 19:09, Tvrtko Ursulin wrote: From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Since yesterday I also briefly tested with Far Cry New Dawn. One run each so possibly doesn't mean anything apart that there isn't a regression aka migration throttling is keeping things at bay even with increased requests to migrate things back to VRAM: before after min/avg/max fps 36/44/54 37/45/55 Cyberpunk 2077 from yesterday was similarly close: 26.96/29.59/30.40 29.70/30.00/30.32 I guess the real story is proper DGPU where misplaced buffers have a real cost. I found one game which regresses spectacularly badly with this series - Assasin's Creed Valhalla. The built-in benchmark at least. The game appears to have a working set much larger than the other games I tested, around 5GiB total during the benchmark. And for some reason migration throttling totally fails to put it in check. I will be investigating this shortly. I think that the conclusion is everything I attempted to add relating to TTM_PL_PREFERRED does not really work as I initially thought it did. Therefore please imagine this series as only containing patches 1, 2 and 5. (And FWIW it was quite annoying to get to the bottom of since for some reason the system exibits some sort of a latching behaviour, where on some boots and/or some minutes of runtime things were fine, and then it would latch onto a mode where the TTM_PL_PREFERRED induced breakage would show. And sometimes this breakage would appear straight away. Odd.) I still need to test though if the subset of patches manage to achieve some positive improvement on their own. It is possible, as patch 5 marks more buffers for re-validation so once overcommit subsides they would get promoted to preferred placement straight away. And 1&2 are notionally fixes for migration throttling so at least in broad sense should be still valid as discussion points. Regards, Tvrtko Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check and see whether there is any improvement. Cc: Christian König Cc: Friedrich Vock Tvrtko Ursulin (5): drm/amdgpu: Fix migration rate limiting accounting drm/amdgpu: Actually respect buffer migration budget drm/ttm: Add preferred placement flag drm/amdgpu: Use preferred placement for VRAM+GTT drm/amdgpu: Re-validate evicted buffers drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 38 +- drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 +++-- drivers/gpu/drm/amd/amdgpu/amdgp
Re: [RFC 0/5] Discussion around eviction improvements
On 09/05/2024 13:40, Tvrtko Ursulin wrote: On 08/05/2024 19:09, Tvrtko Ursulin wrote: From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Since yesterday I also briefly tested with Far Cry New Dawn. One run each so possibly doesn't mean anything apart that there isn't a regression aka migration throttling is keeping things at bay even with increased requests to migrate things back to VRAM: before after min/avg/max fps 36/44/54 37/45/55 Cyberpunk 2077 from yesterday was similarly close: 26.96/29.59/30.40 29.70/30.00/30.32 I guess the real story is proper DGPU where misplaced buffers have a real cost. I found one game which regresses spectacularly badly with this series - Assasin's Creed Valhalla. The built-in benchmark at least. The game appears to have a working set much larger than the other games I tested, around 5GiB total during the benchmark. And for some reason migration throttling totally fails to put it in check. I will be investigating this shortly. Regards, Tvrtko Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check and see whether there is any improvement. Cc: Christian König Cc: Friedrich Vock Tvrtko Ursulin (5): drm/amdgpu: Fix migration rate limiting accounting drm/amdgpu: Actually respect buffer migration budget drm/ttm: Add preferred placement flag drm/amdgpu: Use preferred placement for VRAM+GTT drm/amdgpu: Re-validate evicted buffers drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 38 +- drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 +++-- drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 21 ++-- drivers/gpu/drm/ttm/ttm_resource.c | 13 +--- include/drm/ttm/ttm_placement.h | 3 ++ 5 files changed, 65 insertions(+), 18 deletions(-)
Re: [RFC 0/5] Discussion around eviction improvements
Just FYI, I've been on sick leave for a while and now trying to catch up. It will probably be at least week until I can look into this again. Sorry, Christian. Am 08.05.24 um 20:09 schrieb Tvrtko Ursulin: From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check and see whether there is any improvement. Cc: Christian König Cc: Friedrich Vock Tvrtko Ursulin (5): drm/amdgpu: Fix migration rate limiting accounting drm/amdgpu: Actually respect buffer migration budget drm/ttm: Add preferred placement flag drm/amdgpu: Use preferred placement for VRAM+GTT drm/amdgpu: Re-validate evicted buffers drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 38 +- drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 +++-- drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 21 ++-- drivers/gpu/drm/ttm/ttm_resource.c | 13 +--- include/drm/ttm/ttm_placement.h| 3 ++ 5 files changed, 65 insertions(+), 18 deletions(-)
Re: [RFC 0/5] Discussion around eviction improvements
On 08/05/2024 19:09, Tvrtko Ursulin wrote: From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Since yesterday I also briefly tested with Far Cry New Dawn. One run each so possibly doesn't mean anything apart that there isn't a regression aka migration throttling is keeping things at bay even with increased requests to migrate things back to VRAM: before after min/avg/max fps 36/44/5437/45/55 Cyberpunk 2077 from yesterday was similarly close: 26.96/29.59/30.40 29.70/30.00/30.32 I guess the real story is proper DGPU where misplaced buffers have a real cost. Regards, Tvrtko Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check and see whether there is any improvement. Cc: Christian König Cc: Friedrich Vock Tvrtko Ursulin (5): drm/amdgpu: Fix migration rate limiting accounting drm/amdgpu: Actually respect buffer migration budget drm/ttm: Add preferred placement flag drm/amdgpu: Use preferred placement for VRAM+GTT drm/amdgpu: Re-validate evicted buffers drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 38 +- drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 +++-- drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 21 ++-- drivers/gpu/drm/ttm/ttm_resource.c | 13 +--- include/drm/ttm/ttm_placement.h| 3 ++ 5 files changed, 65 insertions(+), 18 deletions(-)
[RFC 0/5] Discussion around eviction improvements
From: Tvrtko Ursulin Last few days I was looking at the situation with VRAM over subscription, what happens versus what perhaps should happen. Browsing through the driver and running some simple experiments. I ended up with this patch series which, as a disclaimer, may be completely wrong but as I found some suspicious things, to me at least, I thought it was a good point to stop and request some comments. To perhaps summarise what are the main issues I think I found: * Migration rate limiting does not bother knowing if actual migration happened and so can over-account and unfairly penalise. * Migration rate limiting does not even work, at least not for the common case where userspace configures VRAM+GTT. It thinks it can stop migration attempts by playing with bo->allowed_domains vs bo->preferred domains but, both from the code, and from empirical experiments, I see that not working at all. Both masks are identical so fiddling with them achieves nothing. * Idea of the fallback placement only works when VRAM has free space. As soon as it does not, ttm_resource_compatible is happy to leave the buffers in the secondary placement forever. * Driver thinks it will be re-validating evicted buffers on the next submission but it does not for the very common case of VRAM+GTT because it only checks if current placement is *none* of the preferred placements. All those problems are addressed in individual patches. End result of this series appears to be driver which will try harder to move buffers back into VRAM, but will be (more) correctly throttled in doing so by the existing rate limiting logic. I have run a quick benchmark of Cyberpunk 2077 and cannot say that I saw a change but that could be a good thing too. At least I did not break anything, perhaps.. On one occassion I did see the rate limiting logic get confused while for a period of few minutes it went to a mode where it was constantly giving a high migration budget. But that recovered itself when I switched clients and did not come back so I don't know. If there is something wrong there I don't think it would be caused by any patches in this series. Series is probably rough but should be good enough for dicsussion. I am curious to hear if I identified at least something correctly as a real problem. It would also be good to hear what are the suggested games to check and see whether there is any improvement. Cc: Christian König Cc: Friedrich Vock Tvrtko Ursulin (5): drm/amdgpu: Fix migration rate limiting accounting drm/amdgpu: Actually respect buffer migration budget drm/ttm: Add preferred placement flag drm/amdgpu: Use preferred placement for VRAM+GTT drm/amdgpu: Re-validate evicted buffers drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 38 +- drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 8 +++-- drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 21 ++-- drivers/gpu/drm/ttm/ttm_resource.c | 13 +--- include/drm/ttm/ttm_placement.h| 3 ++ 5 files changed, 65 insertions(+), 18 deletions(-) -- 2.44.0
