[PATCHv2 0/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[PATCHv2 0/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[Sai Prakash Ranjan]

Currently for iommu_unmap() of large scatter-gather list with page size
elements, the majority of time is spent in flushing of partial walks in
__arm_lpae_unmap() which is a VA based TLB invalidation invalidating
page-by-page on iommus like arm-smmu-v2 (TLBIVA) which do not support
range based invalidations like on arm-smmu-v3.2.

For example: to unmap a 32MB scatter-gather list with page size elements
(8192 entries), there are 16->2MB buffer unmaps based on the pgsize (2MB
for 4K granule) and each of 2MB will further result in 512 TLBIVAs (2MB/4K)
resulting in a total of 8192 TLBIVAs (512*16) for 16->2MB causing a huge
overhead.

So instead use tlb_flush_all() callback (TLBIALL/TLBIASID) to invalidate
the entire context for partial walk flush on select few platforms where
cost of over-invalidation is less than unmap latency using the newly
introduced quirk IO_PGTABLE_QUIRK_TLB_INV_ALL. We also do this for
non-strict mode given its all about over-invalidation saving time on
individual unmaps and non-deterministic generally.

For this example of 32MB scatter-gather list unmap, this results in just
16 ASID based TLB invalidations (TLBIASIDs) as opposed to 8192 TLBIVAs
thereby increasing the performance of unmaps drastically.

Test on QTI SM8150 SoC for 10 iterations of iommu_{map_sg}/unmap:
(average over 10 iterations)

Before this optimization:

    size        iommu_map_sg      iommu_unmap
      4K            2.067 us         1.854 us
     64K            9.598 us         8.802 us
      1M          148.890 us       130.718 us
      2M          305.864 us        67.291 us
     12M         1793.604 us       390.838 us
     16M         2386.848 us       518.187 us
     24M         3563.296 us       775.989 us
     32M         4747.171 us      1033.364 us

After this optimization:

    size        iommu_map_sg      iommu_unmap
      4K            1.723 us         1.765 us
     64K            9.880 us         8.869 us
      1M          155.364 us       135.223 us
      2M          303.906 us         5.385 us
     12M         1786.557 us        21.250 us
     16M         2391.890 us        27.437 us
     24M         3570.895 us        39.937 us
     32M         4755.234 us        51.797 us

This is further reduced once the map/unmap_pages() support gets in which
will result in just 1 TLBIASID as compared to 16 TLBIASIDs.

Real world data also shows big difference in unmap performance as below:

There were reports of camera frame drops because of high overhead in
iommu unmap without this optimization because of frequent unmaps issued
by camera of about 100MB/s taking more than 100ms thereby causing frame
drops.

Changes in v2:
 * Add a quirk to choose tlb_flush_all in partial walk flush
 * Set the quirk for QTI SoC implementation

Sai Prakash Ranjan (3):
  iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk
    flush
  iommu/io-pgtable: Optimize partial walk flush for large scatter-gather
    list
  iommu/arm-smmu-qcom: Set IO_PGTABLE_QUIRK_TLB_INV_ALL for QTI SoC impl

 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 11 +++++++++++
 drivers/iommu/io-pgtable-arm.c             |  3 ++-
 include/linux/io-pgtable.h                 | 11 +++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)

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[PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Sai Prakash Ranjan]

Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
with tlb_flush_all() callback in partial walk flush to improve unmap
performance on select few platforms where the cost of over-invalidation
is less than the unmap latency.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
---
 drivers/iommu/io-pgtable-arm.c | 3 ++-
 include/linux/io-pgtable.h     | 5 +++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 87def58e79b5..5d362f2214bd 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -768,7 +768,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
 	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
 			    IO_PGTABLE_QUIRK_NON_STRICT |
 			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
-			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
+			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
+			    IO_PGTABLE_QUIRK_TLB_INV_ALL))
 		return NULL;
 
 	data = arm_lpae_alloc_pgtable(cfg);
diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index 4d40dfa75b55..45441592a0e6 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -82,6 +82,10 @@ struct io_pgtable_cfg {
 	 *
 	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
 	 *	attributes set in the TCR for a non-coherent page-table walker.
+	 *
+	 * IO_PGTABLE_QUIRK_TLB_INV_ALL: Use TLBIALL/TLBIASID to invalidate
+	 *	entire context for partial walk flush to increase unmap
+	 *	performance on select few platforms.
 	 */
 	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
 	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
@@ -89,6 +93,7 @@ struct io_pgtable_cfg {
 	#define IO_PGTABLE_QUIRK_NON_STRICT	BIT(4)
 	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
 	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
+	#define IO_PGTABLE_QUIRK_TLB_INV_ALL	BIT(7)
 	unsigned long			quirks;
 	unsigned long			pgsize_bitmap;
 	unsigned int			ias;
-- 
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Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Robin Murphy]

On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
> with tlb_flush_all() callback in partial walk flush to improve unmap
> performance on select few platforms where the cost of over-invalidation
> is less than the unmap latency.

I still think this doesn't belong anywhere near io-pgtable at all. It's 
a driver-internal decision how exactly it implements a non-leaf 
invalidation, and that may be more complex than a predetermined boolean 
decision. For example, I've just realised for SMMUv3 we can't invalidate 
multiple levels of table at once with a range command, since if we 
assume the whole thing is mapped at worst-case page granularity we may 
fail to invalidate any parts which are mapped as intermediate-level 
blocks. If invalidating a 1GB region (with 4KB granule) means having to 
fall back to 256K non-range commands, we may not want to invalidate by 
VA then, even though doing so for a 2MB region is still optimal.

It's also quite feasible that drivers might want to do this for leaf 
invalidations too - if you don't like issuing 512 commands to invalidate 
2MB, do you like issuing 511 commands to invalidate 2044KB? - and at 
that point the logic really has to be in the driver anyway.

Robin.

> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---
>   drivers/iommu/io-pgtable-arm.c | 3 ++-
>   include/linux/io-pgtable.h     | 5 +++++
>   2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 87def58e79b5..5d362f2214bd 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -768,7 +768,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
>   	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>   			    IO_PGTABLE_QUIRK_NON_STRICT |
>   			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
> -			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
> +			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
> +			    IO_PGTABLE_QUIRK_TLB_INV_ALL))
>   		return NULL;
>   
>   	data = arm_lpae_alloc_pgtable(cfg);
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 4d40dfa75b55..45441592a0e6 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -82,6 +82,10 @@ struct io_pgtable_cfg {
>   	 *
>   	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
>   	 *	attributes set in the TCR for a non-coherent page-table walker.
> +	 *
> +	 * IO_PGTABLE_QUIRK_TLB_INV_ALL: Use TLBIALL/TLBIASID to invalidate
> +	 *	entire context for partial walk flush to increase unmap
> +	 *	performance on select few platforms.
>   	 */
>   	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
>   	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
> @@ -89,6 +93,7 @@ struct io_pgtable_cfg {
>   	#define IO_PGTABLE_QUIRK_NON_STRICT	BIT(4)
>   	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
>   	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
> +	#define IO_PGTABLE_QUIRK_TLB_INV_ALL	BIT(7)
>   	unsigned long			quirks;
>   	unsigned long			pgsize_bitmap;
>   	unsigned int			ias;
> 

Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Sai Prakash Ranjan]

Hi Robin,

On 2021-06-21 21:15, Robin Murphy wrote:
> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
>> with tlb_flush_all() callback in partial walk flush to improve unmap
>> performance on select few platforms where the cost of 
>> over-invalidation
>> is less than the unmap latency.
> 
> I still think this doesn't belong anywhere near io-pgtable at all.
> It's a driver-internal decision how exactly it implements a non-leaf
> invalidation, and that may be more complex than a predetermined
> boolean decision. For example, I've just realised for SMMUv3 we can't
> invalidate multiple levels of table at once with a range command,
> since if we assume the whole thing is mapped at worst-case page
> granularity we may fail to invalidate any parts which are mapped as
> intermediate-level blocks. If invalidating a 1GB region (with 4KB
> granule) means having to fall back to 256K non-range commands, we may
> not want to invalidate by VA then, even though doing so for a 2MB
> region is still optimal.
> 
> It's also quite feasible that drivers might want to do this for leaf
> invalidations too - if you don't like issuing 512 commands to
> invalidate 2MB, do you like issuing 511 commands to invalidate 2044KB?
> - and at that point the logic really has to be in the driver anyway.
> 

Ok I will move this to tlb_flush_walk() functions in the drivers. In the 
previous
v1 thread, you suggested to make the choice in iommu_get_dma_strict() 
test,
I assume you meant the test in iommu_dma_init_domain() with a flag or 
was it
the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
init_domain?

I am still a bit confused on where this flag would be? Should this be a 
part
of struct iommu_domain?

Thanks,
Sai

> 
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> ---
>>   drivers/iommu/io-pgtable-arm.c | 3 ++-
>>   include/linux/io-pgtable.h     | 5 +++++
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>> b/drivers/iommu/io-pgtable-arm.c
>> index 87def58e79b5..5d362f2214bd 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -768,7 +768,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg 
>> *cfg, void *cookie)
>>   	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>>   			    IO_PGTABLE_QUIRK_NON_STRICT |
>>   			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
>> -			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
>> +			    IO_PGTABLE_QUIRK_ARM_OUTER_WBWA |
>> +			    IO_PGTABLE_QUIRK_TLB_INV_ALL))
>>   		return NULL;
>>     	data = arm_lpae_alloc_pgtable(cfg);
>> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
>> index 4d40dfa75b55..45441592a0e6 100644
>> --- a/include/linux/io-pgtable.h
>> +++ b/include/linux/io-pgtable.h
>> @@ -82,6 +82,10 @@ struct io_pgtable_cfg {
>>   	 *
>>   	 * IO_PGTABLE_QUIRK_ARM_OUTER_WBWA: Override the outer-cacheability
>>   	 *	attributes set in the TCR for a non-coherent page-table walker.
>> +	 *
>> +	 * IO_PGTABLE_QUIRK_TLB_INV_ALL: Use TLBIALL/TLBIASID to invalidate
>> +	 *	entire context for partial walk flush to increase unmap
>> +	 *	performance on select few platforms.
>>   	 */
>>   	#define IO_PGTABLE_QUIRK_ARM_NS		BIT(0)
>>   	#define IO_PGTABLE_QUIRK_NO_PERMS	BIT(1)
>> @@ -89,6 +93,7 @@ struct io_pgtable_cfg {
>>   	#define IO_PGTABLE_QUIRK_NON_STRICT	BIT(4)
>>   	#define IO_PGTABLE_QUIRK_ARM_TTBR1	BIT(5)
>>   	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA	BIT(6)
>> +	#define IO_PGTABLE_QUIRK_TLB_INV_ALL	BIT(7)
>>   	unsigned long			quirks;
>>   	unsigned long			pgsize_bitmap;
>>   	unsigned int			ias;
>> 

-- 
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member
of Code Aurora Forum, hosted by The Linux Foundation

Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Robin Murphy]

On 2021-06-22 08:11, Sai Prakash Ranjan wrote:
> Hi Robin,
> 
> On 2021-06-21 21:15, Robin Murphy wrote:
>> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
>>> with tlb_flush_all() callback in partial walk flush to improve unmap
>>> performance on select few platforms where the cost of over-invalidation
>>> is less than the unmap latency.
>>
>> I still think this doesn't belong anywhere near io-pgtable at all.
>> It's a driver-internal decision how exactly it implements a non-leaf
>> invalidation, and that may be more complex than a predetermined
>> boolean decision. For example, I've just realised for SMMUv3 we can't
>> invalidate multiple levels of table at once with a range command,
>> since if we assume the whole thing is mapped at worst-case page
>> granularity we may fail to invalidate any parts which are mapped as
>> intermediate-level blocks. If invalidating a 1GB region (with 4KB
>> granule) means having to fall back to 256K non-range commands, we may
>> not want to invalidate by VA then, even though doing so for a 2MB
>> region is still optimal.
>>
>> It's also quite feasible that drivers might want to do this for leaf
>> invalidations too - if you don't like issuing 512 commands to
>> invalidate 2MB, do you like issuing 511 commands to invalidate 2044KB?
>> - and at that point the logic really has to be in the driver anyway.
>>
> 
> Ok I will move this to tlb_flush_walk() functions in the drivers. In the 
> previous
> v1 thread, you suggested to make the choice in iommu_get_dma_strict() test,
> I assume you meant the test in iommu_dma_init_domain() with a flag or 
> was it
> the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
> init_domain?

Yes, I meant literally inside the same condition where we currently set 
"pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;" in 
arm_smmu_init_domain_context().

> I am still a bit confused on where this flag would be? Should this be a 
> part
> of struct iommu_domain?

Well, if you were to rewrite the config with an alternative set of 
flush_ops at that point it would be implicit. For a flag, probably 
either in arm_smmu_domain or arm_smmu_impl. Maybe a flag would be less 
useful than generalising straight to a "maximum number of by-VA 
invalidations it's worth sending individually" threshold value? It's 
clear to me what overall shape and separation of responsibility is most 
logical, but beyond that I don't have a particularly strong opinion on 
the exact implementation; I've just been chucking ideas around :)

Cheers,
Robin.

Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Sai Prakash Ranjan]

Hi Robin,

On 2021-06-22 17:41, Robin Murphy wrote:
> On 2021-06-22 08:11, Sai Prakash Ranjan wrote:
>> Hi Robin,
>> 
>> On 2021-06-21 21:15, Robin Murphy wrote:
>>> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>>>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire 
>>>> context
>>>> with tlb_flush_all() callback in partial walk flush to improve unmap
>>>> performance on select few platforms where the cost of 
>>>> over-invalidation
>>>> is less than the unmap latency.
>>> 
>>> I still think this doesn't belong anywhere near io-pgtable at all.
>>> It's a driver-internal decision how exactly it implements a non-leaf
>>> invalidation, and that may be more complex than a predetermined
>>> boolean decision. For example, I've just realised for SMMUv3 we can't
>>> invalidate multiple levels of table at once with a range command,
>>> since if we assume the whole thing is mapped at worst-case page
>>> granularity we may fail to invalidate any parts which are mapped as
>>> intermediate-level blocks. If invalidating a 1GB region (with 4KB
>>> granule) means having to fall back to 256K non-range commands, we may
>>> not want to invalidate by VA then, even though doing so for a 2MB
>>> region is still optimal.
>>> 
>>> It's also quite feasible that drivers might want to do this for leaf
>>> invalidations too - if you don't like issuing 512 commands to
>>> invalidate 2MB, do you like issuing 511 commands to invalidate 
>>> 2044KB?
>>> - and at that point the logic really has to be in the driver anyway.
>>> 
>> 
>> Ok I will move this to tlb_flush_walk() functions in the drivers. In 
>> the previous
>> v1 thread, you suggested to make the choice in iommu_get_dma_strict() 
>> test,
>> I assume you meant the test in iommu_dma_init_domain() with a flag or 
>> was it
>> the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
>> init_domain?
> 
> Yes, I meant literally inside the same condition where we currently
> set "pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;" in
> arm_smmu_init_domain_context().
> 

Ok got it, thanks.

>> I am still a bit confused on where this flag would be? Should this be 
>> a part
>> of struct iommu_domain?
> 
> Well, if you were to rewrite the config with an alternative set of
> flush_ops at that point it would be implicit. For a flag, probably
> either in arm_smmu_domain or arm_smmu_impl. Maybe a flag would be less
> useful than generalising straight to a "maximum number of by-VA
> invalidations it's worth sending individually" threshold value?

But then we would still need some flag to make this implementation
specific (qcom specific for now) and this threshold would just be
another condition although it would have been useful if this was
generic enough.

> It's clear to me what overall shape and separation of responsibility is
> most logical, but beyond that I don't have a particularly strong
> opinion on the exact implementation; I've just been chucking ideas
> around :)
> 

Your ideas are very informative and useful :)

Thanks,
Sai

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Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Robin Murphy]

On 2021-06-22 15:27, Sai Prakash Ranjan wrote:
> Hi Robin,
> 
> On 2021-06-22 17:41, Robin Murphy wrote:
>> On 2021-06-22 08:11, Sai Prakash Ranjan wrote:
>>> Hi Robin,
>>>
>>> On 2021-06-21 21:15, Robin Murphy wrote:
>>>> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>>>>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire context
>>>>> with tlb_flush_all() callback in partial walk flush to improve unmap
>>>>> performance on select few platforms where the cost of 
>>>>> over-invalidation
>>>>> is less than the unmap latency.
>>>>
>>>> I still think this doesn't belong anywhere near io-pgtable at all.
>>>> It's a driver-internal decision how exactly it implements a non-leaf
>>>> invalidation, and that may be more complex than a predetermined
>>>> boolean decision. For example, I've just realised for SMMUv3 we can't
>>>> invalidate multiple levels of table at once with a range command,
>>>> since if we assume the whole thing is mapped at worst-case page
>>>> granularity we may fail to invalidate any parts which are mapped as
>>>> intermediate-level blocks. If invalidating a 1GB region (with 4KB
>>>> granule) means having to fall back to 256K non-range commands, we may
>>>> not want to invalidate by VA then, even though doing so for a 2MB
>>>> region is still optimal.
>>>>
>>>> It's also quite feasible that drivers might want to do this for leaf
>>>> invalidations too - if you don't like issuing 512 commands to
>>>> invalidate 2MB, do you like issuing 511 commands to invalidate 2044KB?
>>>> - and at that point the logic really has to be in the driver anyway.
>>>>
>>>
>>> Ok I will move this to tlb_flush_walk() functions in the drivers. In 
>>> the previous
>>> v1 thread, you suggested to make the choice in iommu_get_dma_strict() 
>>> test,
>>> I assume you meant the test in iommu_dma_init_domain() with a flag or 
>>> was it
>>> the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
>>> init_domain?
>>
>> Yes, I meant literally inside the same condition where we currently
>> set "pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;" in
>> arm_smmu_init_domain_context().
>>
> 
> Ok got it, thanks.
> 
>>> I am still a bit confused on where this flag would be? Should this be 
>>> a part
>>> of struct iommu_domain?
>>
>> Well, if you were to rewrite the config with an alternative set of
>> flush_ops at that point it would be implicit. For a flag, probably
>> either in arm_smmu_domain or arm_smmu_impl. Maybe a flag would be less
>> useful than generalising straight to a "maximum number of by-VA
>> invalidations it's worth sending individually" threshold value?
> 
> But then we would still need some flag to make this implementation
> specific (qcom specific for now) and this threshold would just be
> another condition although it would have been useful if this was
> generic enough.

Well, for that approach I assume we could do something like special-case 
0, or if it's a mutable per-domain value maybe just initialise it to 
SIZE_MAX or whatever such that it would never be reached in practice. 
Whichever way, it was meant to be implied that anything at the domain 
level would still be subject to final adjustment by the init_context hook.

Robin.

>> It's clear to me what overall shape and separation of responsibility is
>> most logical, but beyond that I don't have a particularly strong
>> opinion on the exact implementation; I've just been chucking ideas
>> around :)
>>
> 
> Your ideas are very informative and useful :)
> 
> Thanks,
> Sai
> 

Re: [PATCHv2 1/3] iommu/io-pgtable: Add a quirk to use tlb_flush_all() for partial walk flush

[Sai Prakash Ranjan]

Hi Robin,

On 2021-06-23 00:07, Robin Murphy wrote:
> On 2021-06-22 15:27, Sai Prakash Ranjan wrote:
>> Hi Robin,
>> 
>> On 2021-06-22 17:41, Robin Murphy wrote:
>>> On 2021-06-22 08:11, Sai Prakash Ranjan wrote:
>>>> Hi Robin,
>>>> 
>>>> On 2021-06-21 21:15, Robin Murphy wrote:
>>>>> On 2021-06-18 03:51, Sai Prakash Ranjan wrote:
>>>>>> Add a quirk IO_PGTABLE_QUIRK_TLB_INV_ALL to invalidate entire 
>>>>>> context
>>>>>> with tlb_flush_all() callback in partial walk flush to improve 
>>>>>> unmap
>>>>>> performance on select few platforms where the cost of 
>>>>>> over-invalidation
>>>>>> is less than the unmap latency.
>>>>> 
>>>>> I still think this doesn't belong anywhere near io-pgtable at all.
>>>>> It's a driver-internal decision how exactly it implements a 
>>>>> non-leaf
>>>>> invalidation, and that may be more complex than a predetermined
>>>>> boolean decision. For example, I've just realised for SMMUv3 we 
>>>>> can't
>>>>> invalidate multiple levels of table at once with a range command,
>>>>> since if we assume the whole thing is mapped at worst-case page
>>>>> granularity we may fail to invalidate any parts which are mapped as
>>>>> intermediate-level blocks. If invalidating a 1GB region (with 4KB
>>>>> granule) means having to fall back to 256K non-range commands, we 
>>>>> may
>>>>> not want to invalidate by VA then, even though doing so for a 2MB
>>>>> region is still optimal.
>>>>> 
>>>>> It's also quite feasible that drivers might want to do this for 
>>>>> leaf
>>>>> invalidations too - if you don't like issuing 512 commands to
>>>>> invalidate 2MB, do you like issuing 511 commands to invalidate 
>>>>> 2044KB?
>>>>> - and at that point the logic really has to be in the driver 
>>>>> anyway.
>>>>> 
>>>> 
>>>> Ok I will move this to tlb_flush_walk() functions in the drivers. In 
>>>> the previous
>>>> v1 thread, you suggested to make the choice in 
>>>> iommu_get_dma_strict() test,
>>>> I assume you meant the test in iommu_dma_init_domain() with a flag 
>>>> or was it
>>>> the leaf driver(ex:arm-smmu.c) test of iommu_get_dma_strict() in 
>>>> init_domain?
>>> 
>>> Yes, I meant literally inside the same condition where we currently
>>> set "pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;" in
>>> arm_smmu_init_domain_context().
>>> 
>> 
>> Ok got it, thanks.
>> 
>>>> I am still a bit confused on where this flag would be? Should this 
>>>> be a part
>>>> of struct iommu_domain?
>>> 
>>> Well, if you were to rewrite the config with an alternative set of
>>> flush_ops at that point it would be implicit. For a flag, probably
>>> either in arm_smmu_domain or arm_smmu_impl. Maybe a flag would be 
>>> less
>>> useful than generalising straight to a "maximum number of by-VA
>>> invalidations it's worth sending individually" threshold value?
>> 
>> But then we would still need some flag to make this implementation
>> specific (qcom specific for now) and this threshold would just be
>> another condition although it would have been useful if this was
>> generic enough.
> 
> Well, for that approach I assume we could do something like
> special-case 0, or if it's a mutable per-domain value maybe just
> initialise it to SIZE_MAX or whatever such that it would never be
> reached in practice. Whichever way, it was meant to be implied that
> anything at the domain level would still be subject to final
> adjustment by the init_context hook.
> 

Ok that should work, so I went ahead with another set of flush_ops
and posted out v3.

Thanks,
Sai

> 
>>> It's clear to me what overall shape and separation of responsibility 
>>> is
>>> most logical, but beyond that I don't have a particularly strong
>>> opinion on the exact implementation; I've just been chucking ideas
>>> around :)
>>> 
>> 
>> Your ideas are very informative and useful :)
>> 
>> Thanks,
>> Sai
>> 

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[PATCHv2 2/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[Sai Prakash Ranjan]

Currently for iommu_unmap() of large scatter-gather list with page size
elements, the majority of time is spent in flushing of partial walks in
__arm_lpae_unmap() which is a VA based TLB invalidation invalidating
page-by-page on iommus like arm-smmu-v2 (TLBIVA) which do not support
range based invalidations like on arm-smmu-v3.2.

For example: to unmap a 32MB scatter-gather list with page size elements
(8192 entries), there are 16->2MB buffer unmaps based on the pgsize (2MB
for 4K granule) and each of 2MB will further result in 512 TLBIVAs (2MB/4K)
resulting in a total of 8192 TLBIVAs (512*16) for 16->2MB causing a huge
overhead.

So instead use tlb_flush_all() callback (TLBIALL/TLBIASID) to invalidate
the entire context for partial walk flush on select few platforms where
cost of over-invalidation is less than unmap latency using the newly
introduced quirk IO_PGTABLE_QUIRK_TLB_INV_ALL. We also do this for
non-strict mode given its all about over-invalidation saving time on
individual unmaps and non-deterministic generally.

For this example of 32MB scatter-gather list unmap, this results in just
16 ASID based TLB invalidations (TLBIASIDs) as opposed to 8192 TLBIVAs
thereby increasing the performance of unmaps drastically.

Test on QTI SM8150 SoC for 10 iterations of iommu_{map_sg}/unmap:
(average over 10 iterations)

Before this optimization:

    size        iommu_map_sg      iommu_unmap
      4K            2.067 us         1.854 us
     64K            9.598 us         8.802 us
      1M          148.890 us       130.718 us
      2M          305.864 us        67.291 us
     12M         1793.604 us       390.838 us
     16M         2386.848 us       518.187 us
     24M         3563.296 us       775.989 us
     32M         4747.171 us      1033.364 us

After this optimization:

    size        iommu_map_sg      iommu_unmap
      4K            1.723 us         1.765 us
     64K            9.880 us         8.869 us
      1M          155.364 us       135.223 us
      2M          303.906 us         5.385 us
     12M         1786.557 us        21.250 us
     16M         2391.890 us        27.437 us
     24M         3570.895 us        39.937 us
     32M         4755.234 us        51.797 us

This is further reduced once the map/unmap_pages() support gets in which
will result in just 1 TLBIASID as compared to 16 TLBIASIDs.

Real world data also shows big difference in unmap performance as below:

There were reports of camera frame drops because of high overhead in
iommu unmap without this optimization because of frequent unmaps issued
by camera of about 100MB/s taking more than 100ms thereby causing frame
drops.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
---
 include/linux/io-pgtable.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index 45441592a0e6..fd6b30cfdbf7 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -219,6 +219,12 @@ static inline void
 io_pgtable_tlb_flush_walk(struct io_pgtable *iop, unsigned long iova,
 			  size_t size, size_t granule)
 {
+	if (iop->cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT ||
+	    iop->cfg.quirks & IO_PGTABLE_QUIRK_TLB_INV_ALL) {
+		iop->cfg.tlb->tlb_flush_all(iop->cookie);
+		return;
+	}
+
 	if (iop->cfg.tlb && iop->cfg.tlb->tlb_flush_walk)
 		iop->cfg.tlb->tlb_flush_walk(iova, size, granule, iop->cookie);
 }
-- 
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Re: [PATCHv2 2/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[Doug Anderson]

Hi,

On Thu, Jun 17, 2021 at 7:51 PM Sai Prakash Ranjan
<saiprakash.ranjan@codeaurora.org> wrote:
>
> Currently for iommu_unmap() of large scatter-gather list with page size
> elements, the majority of time is spent in flushing of partial walks in
> __arm_lpae_unmap() which is a VA based TLB invalidation invalidating
> page-by-page on iommus like arm-smmu-v2 (TLBIVA) which do not support
> range based invalidations like on arm-smmu-v3.2.
>
> For example: to unmap a 32MB scatter-gather list with page size elements
> (8192 entries), there are 16->2MB buffer unmaps based on the pgsize (2MB
> for 4K granule) and each of 2MB will further result in 512 TLBIVAs (2MB/4K)
> resulting in a total of 8192 TLBIVAs (512*16) for 16->2MB causing a huge
> overhead.
>
> So instead use tlb_flush_all() callback (TLBIALL/TLBIASID) to invalidate
> the entire context for partial walk flush on select few platforms where
> cost of over-invalidation is less than unmap latency

It would probably be worth punching this description up a little bit.
Elsewhere you said in more detail why this over-invalidation is less
of a big deal for the Qualcomm SMMU. It's probably worth saying
something like that here, too. Like this bit paraphrased from your
other email:

On qcom impl, we have several performance improvements for TLB cache
invalidations in HW like wait-for-safe (for realtime clients such as
camera and display) and few others to allow for cache lookups/updates
when TLBI is in progress for the same context bank.


> using the newly
> introduced quirk IO_PGTABLE_QUIRK_TLB_INV_ALL. We also do this for
> non-strict mode given its all about over-invalidation saving time on
> individual unmaps and non-deterministic generally.

As per usual I'm mostly clueless, but I don't quite understand why you
want this new behavior for non-strict mode. To me it almost seems like
the opposite? Specifically, non-strict mode is already outside the
critical path today and so there's no need to optimize it. I'm
probably not explaining myself clearly, but I guess i'm thinking:

a) today for strict, unmap is in the critical path and it's important
to get it out of there. Getting it out of the critical path is so
important that we're willing to over-invalidate to speed up the
critical path.

b) today for non-strict, unmap is not in the critical path.

So I would almost expect your patch to _disable_ your new feature for
non-strict mappings, not auto-enable your new feature for non-strict
mappings.

If I'm babbling, feel free to ignore. ;-) Looking back, I guess Robin
was the one that suggested the behavior you're implementing, so it's
more likely he's right than I am. ;-)


-Doug

Re: [PATCHv2 2/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[Sai Prakash Ranjan]

Hi,

On 2021-06-19 03:39, Doug Anderson wrote:
> Hi,
> 
> On Thu, Jun 17, 2021 at 7:51 PM Sai Prakash Ranjan
> <saiprakash.ranjan@codeaurora.org> wrote:
>> 
>> Currently for iommu_unmap() of large scatter-gather list with page 
>> size
>> elements, the majority of time is spent in flushing of partial walks 
>> in
>> __arm_lpae_unmap() which is a VA based TLB invalidation invalidating
>> page-by-page on iommus like arm-smmu-v2 (TLBIVA) which do not support
>> range based invalidations like on arm-smmu-v3.2.
>> 
>> For example: to unmap a 32MB scatter-gather list with page size 
>> elements
>> (8192 entries), there are 16->2MB buffer unmaps based on the pgsize 
>> (2MB
>> for 4K granule) and each of 2MB will further result in 512 TLBIVAs 
>> (2MB/4K)
>> resulting in a total of 8192 TLBIVAs (512*16) for 16->2MB causing a 
>> huge
>> overhead.
>> 
>> So instead use tlb_flush_all() callback (TLBIALL/TLBIASID) to 
>> invalidate
>> the entire context for partial walk flush on select few platforms 
>> where
>> cost of over-invalidation is less than unmap latency
> 
> It would probably be worth punching this description up a little bit.
> Elsewhere you said in more detail why this over-invalidation is less
> of a big deal for the Qualcomm SMMU. It's probably worth saying
> something like that here, too. Like this bit paraphrased from your
> other email:
> 
> On qcom impl, we have several performance improvements for TLB cache
> invalidations in HW like wait-for-safe (for realtime clients such as
> camera and display) and few others to allow for cache lookups/updates
> when TLBI is in progress for the same context bank.
> 

Sure will add this info as well in the next version.

> 
>> using the newly
>> introduced quirk IO_PGTABLE_QUIRK_TLB_INV_ALL. We also do this for
>> non-strict mode given its all about over-invalidation saving time on
>> individual unmaps and non-deterministic generally.
> 
> As per usual I'm mostly clueless, but I don't quite understand why you
> want this new behavior for non-strict mode. To me it almost seems like
> the opposite? Specifically, non-strict mode is already outside the
> critical path today and so there's no need to optimize it. I'm
> probably not explaining myself clearly, but I guess i'm thinking:
> 
> a) today for strict, unmap is in the critical path and it's important
> to get it out of there. Getting it out of the critical path is so
> important that we're willing to over-invalidate to speed up the
> critical path.
> 
> b) today for non-strict, unmap is not in the critical path.
> 
> So I would almost expect your patch to _disable_ your new feature for
> non-strict mappings, not auto-enable your new feature for non-strict
> mappings.
> 
> If I'm babbling, feel free to ignore. ;-) Looking back, I guess Robin
> was the one that suggested the behavior you're implementing, so it's
> more likely he's right than I am. ;-)
> 

Thanks for taking a look. Non-strict mode is only for leaf entries and
dma domains and this optimization is for non-leaf entries and is 
applicable
for both, see __arm_lpae_unmap(). In other words, if you have 
iommu.strict=0
(non-strict mode) and try unmapping a large sg buffer as the problem 
described
in the commit text, you would still go via this path in unmap and see 
the
delay without this patch. So what Robin suggested is that, let's do this
unconditionally for all users with non-strict mode as opposed to only
restricting it to implementation specific in case of strict mode.

Thanks,
Sai

-- 
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member
of Code Aurora Forum, hosted by The Linux Foundation

Re: [PATCHv2 2/3] iommu/io-pgtable: Optimize partial walk flush for large scatter-gather list

[Robin Murphy]

On 2021-06-21 06:47, Sai Prakash Ranjan wrote:
> Hi,
> 
> On 2021-06-19 03:39, Doug Anderson wrote:
>> Hi,
>>
>> On Thu, Jun 17, 2021 at 7:51 PM Sai Prakash Ranjan
>> <saiprakash.ranjan@codeaurora.org> wrote:
>>>
>>> Currently for iommu_unmap() of large scatter-gather list with page size
>>> elements, the majority of time is spent in flushing of partial walks in
>>> __arm_lpae_unmap() which is a VA based TLB invalidation invalidating
>>> page-by-page on iommus like arm-smmu-v2 (TLBIVA) which do not support
>>> range based invalidations like on arm-smmu-v3.2.
>>>
>>> For example: to unmap a 32MB scatter-gather list with page size elements
>>> (8192 entries), there are 16->2MB buffer unmaps based on the pgsize (2MB
>>> for 4K granule) and each of 2MB will further result in 512 TLBIVAs 
>>> (2MB/4K)
>>> resulting in a total of 8192 TLBIVAs (512*16) for 16->2MB causing a huge
>>> overhead.
>>>
>>> So instead use tlb_flush_all() callback (TLBIALL/TLBIASID) to invalidate
>>> the entire context for partial walk flush on select few platforms where
>>> cost of over-invalidation is less than unmap latency
>>
>> It would probably be worth punching this description up a little bit.
>> Elsewhere you said in more detail why this over-invalidation is less
>> of a big deal for the Qualcomm SMMU. It's probably worth saying
>> something like that here, too. Like this bit paraphrased from your
>> other email:
>>
>> On qcom impl, we have several performance improvements for TLB cache
>> invalidations in HW like wait-for-safe (for realtime clients such as
>> camera and display) and few others to allow for cache lookups/updates
>> when TLBI is in progress for the same context bank.
>>
> 
> Sure will add this info as well in the next version.
> 
>>
>>> using the newly
>>> introduced quirk IO_PGTABLE_QUIRK_TLB_INV_ALL. We also do this for
>>> non-strict mode given its all about over-invalidation saving time on
>>> individual unmaps and non-deterministic generally.
>>
>> As per usual I'm mostly clueless, but I don't quite understand why you
>> want this new behavior for non-strict mode. To me it almost seems like
>> the opposite? Specifically, non-strict mode is already outside the
>> critical path today and so there's no need to optimize it. I'm
>> probably not explaining myself clearly, but I guess i'm thinking:
>>
>> a) today for strict, unmap is in the critical path and it's important
>> to get it out of there. Getting it out of the critical path is so
>> important that we're willing to over-invalidate to speed up the
>> critical path.
>>
>> b) today for non-strict, unmap is not in the critical path.
>>
>> So I would almost expect your patch to _disable_ your new feature for
>> non-strict mappings, not auto-enable your new feature for non-strict
>> mappings.
>>
>> If I'm babbling, feel free to ignore. ;-) Looking back, I guess Robin
>> was the one that suggested the behavior you're implementing, so it's
>> more likely he's right than I am. ;-)
>>
> 
> Thanks for taking a look. Non-strict mode is only for leaf entries and
> dma domains and this optimization is for non-leaf entries and is applicable
> for both, see __arm_lpae_unmap(). In other words, if you have 
> iommu.strict=0
> (non-strict mode) and try unmapping a large sg buffer as the problem 
> described
> in the commit text, you would still go via this path in unmap and see the
> delay without this patch. So what Robin suggested is that, let's do this
> unconditionally for all users with non-strict mode as opposed to only
> restricting it to implementation specific in case of strict mode.

Right, unmapping tables works out as a bit of a compromise for 
non-strict mode - we don't use a freelist to defer the freeing of 
pagetable pages, so we rely on making non-leaf invalidations 
synchronously to knock out walk caches which may be pointing to the page 
beforte we free it. We might actually be able to get away without that 
for non-strict unmaps, since partial walks pointing at freed memory 
probably aren't too much more hazardous than the equivalent leaf TLB 
entries while the IOVA region is held in the flush queue, but it 
certainly does matter for maps when we're knocking out a (presumably 
empty) table entry to put down a new block whose IOVA will be 
immediately live.

Robin.

[PATCHv2 3/3] iommu/arm-smmu-qcom: Set IO_PGTABLE_QUIRK_TLB_INV_ALL for QTI SoC impl

[Sai Prakash Ranjan]

Set the pgtable quirk IO_PGTABLE_QUIRK_TLB_INV_ALL for QTI SoC
implementation to use ::tlb_flush_all() for partial walk flush
to improve unmap performance.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
---
 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index 7771d40176de..b8ae51592d00 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -146,6 +146,8 @@ static int qcom_adreno_smmu_init_context(struct arm_smmu_domain *smmu_domain,
 {
 	struct adreno_smmu_priv *priv;
 
+	pgtbl_cfg->quirks |= IO_PGTABLE_QUIRK_TLB_INV_ALL;
+
 	/* Only enable split pagetables for the GPU device (SID 0) */
 	if (!qcom_adreno_smmu_is_gpu_device(dev))
 		return 0;
@@ -185,6 +187,14 @@ static const struct of_device_id qcom_smmu_client_of_match[] __maybe_unused = {
 	{ }
 };
 
+static int qcom_smmu_init_context(struct arm_smmu_domain *smmu_domain,
+		struct io_pgtable_cfg *pgtbl_cfg, struct device *dev)
+{
+	pgtbl_cfg->quirks |= IO_PGTABLE_QUIRK_TLB_INV_ALL;
+
+	return 0;
+}
+
 static int qcom_smmu_cfg_probe(struct arm_smmu_device *smmu)
 {
 	unsigned int last_s2cr = ARM_SMMU_GR0_S2CR(smmu->num_mapping_groups - 1);
@@ -308,6 +318,7 @@ static int qcom_smmu500_reset(struct arm_smmu_device *smmu)
 }
 
 static const struct arm_smmu_impl qcom_smmu_impl = {
+	.init_context = qcom_smmu_init_context,
 	.cfg_probe = qcom_smmu_cfg_probe,
 	.def_domain_type = qcom_smmu_def_domain_type,
 	.reset = qcom_smmu500_reset,
-- 
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