[PATCH 1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[PATCH 1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[Alistair Popple]

The NPU has a limited number of address translation shootdown (ATSD)
registers and the GPU has limited bandwidth to process ATSDs. This can
result in contention of ATSD registers leading to soft lockups on some
threads, particularly when invalidating a large address range in
pnv_npu2_mn_invalidate_range().

At some threshold it becomes more efficient to flush the entire GPU TLB for
the given MM context (PID) than individually flushing each address in the
range. This patch will result in ranges greater than 2MB being converted
from 32+ ATSDs into a single ATSD which will flush the TLB for the given
PID on each GPU.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
---
 arch/powerpc/platforms/powernv/npu-dma.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
index 94801d8e7894..dc34662e9df9 100644
--- a/arch/powerpc/platforms/powernv/npu-dma.c
+++ b/arch/powerpc/platforms/powernv/npu-dma.c
@@ -40,6 +40,13 @@
 DEFINE_SPINLOCK(npu_context_lock);
 
 /*
+ * When an address shootdown range exceeds this threshold we invalidate the
+ * entire TLB on the GPU for the given PID rather than each specific address in
+ * the range.
+ */
+#define ATSD_THRESHOLD (2*1024*1024)
+
+/*
  * Other types of TCE cache invalidation are not functional in the
  * hardware.
  */
@@ -675,11 +682,19 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
 	struct npu_context *npu_context = mn_to_npu_context(mn);
 	unsigned long address;
 
-	for (address = start; address < end; address += PAGE_SIZE)
-		mmio_invalidate(npu_context, 1, address, false);
+	if (end - start > ATSD_THRESHOLD) {
+		/*
+		 * Just invalidate the entire PID if the address range is too
+		 * large.
+		 */
+		mmio_invalidate(npu_context, 0, 0, true);
+	} else {
+		for (address = start; address < end; address += PAGE_SIZE)
+			mmio_invalidate(npu_context, 1, address, false);
 
-	/* Do the flush only on the final addess == end */
-	mmio_invalidate(npu_context, 1, address, true);
+		/* Do the flush only on the final addess == end */
+		mmio_invalidate(npu_context, 1, address, true);
+	}
 }
 
 static const struct mmu_notifier_ops nv_nmmu_notifier_ops = {
-- 
2.11.0

[PATCH 2/2] powernv/npu: Add a debugfs setting to change ATSD threshold

[Alistair Popple]

The threshold at which it becomes more efficient to coalesce a range of
ATSDs into a single per-PID ATSD is currently not well understood due to a
lack of real-world work loads. This patch adds a debugfs parameter allowing
the threshold to be altered at runtime in order to aid future development
and refinement of the value.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
---
 arch/powerpc/platforms/powernv/npu-dma.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
index dc34662e9df9..a765bf576c14 100644
--- a/arch/powerpc/platforms/powernv/npu-dma.c
+++ b/arch/powerpc/platforms/powernv/npu-dma.c
@@ -17,7 +17,9 @@
 #include <linux/pci.h>
 #include <linux/memblock.h>
 #include <linux/iommu.h>
+#include <linux/debugfs.h>
 
+#include <asm/debugfs.h>
 #include <asm/tlb.h>
 #include <asm/powernv.h>
 #include <asm/reg.h>
@@ -44,7 +46,8 @@ DEFINE_SPINLOCK(npu_context_lock);
  * entire TLB on the GPU for the given PID rather than each specific address in
  * the range.
  */
-#define ATSD_THRESHOLD (2*1024*1024)
+static uint64_t atsd_threshold = 2 * 1024 * 1024;
+static struct dentry *atsd_threshold_dentry;
 
 /*
  * Other types of TCE cache invalidation are not functional in the
@@ -682,7 +685,7 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
 	struct npu_context *npu_context = mn_to_npu_context(mn);
 	unsigned long address;
 
-	if (end - start > ATSD_THRESHOLD) {
+	if (end - start > atsd_threshold) {
 		/*
 		 * Just invalidate the entire PID if the address range is too
 		 * large.
@@ -956,6 +959,11 @@ int pnv_npu2_init(struct pnv_phb *phb)
 	static int npu_index;
 	uint64_t rc = 0;
 
+	if (!atsd_threshold_dentry) {
+		atsd_threshold_dentry = debugfs_create_x64("atsd_threshold",
+				   0600, powerpc_debugfs_root, &atsd_threshold);
+	}
+
 	phb->npu.nmmu_flush =
 		of_property_read_bool(phb->hose->dn, "ibm,nmmu-flush");
 	for_each_child_of_node(phb->hose->dn, dn) {
-- 
2.11.0

Re: [PATCH 1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[Balbir Singh]

On Tue, Apr 17, 2018 at 7:11 PM, Alistair Popple <alistair@popple.id.au> wrote:
> The NPU has a limited number of address translation shootdown (ATSD)
> registers and the GPU has limited bandwidth to process ATSDs. This can
> result in contention of ATSD registers leading to soft lockups on some
> threads, particularly when invalidating a large address range in
> pnv_npu2_mn_invalidate_range().
>
> At some threshold it becomes more efficient to flush the entire GPU TLB for
> the given MM context (PID) than individually flushing each address in the
> range. This patch will result in ranges greater than 2MB being converted
> from 32+ ATSDs into a single ATSD which will flush the TLB for the given
> PID on each GPU.
>
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> ---
>  arch/powerpc/platforms/powernv/npu-dma.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> index 94801d8e7894..dc34662e9df9 100644
> --- a/arch/powerpc/platforms/powernv/npu-dma.c
> +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> @@ -40,6 +40,13 @@
>  DEFINE_SPINLOCK(npu_context_lock);
>
>  /*
> + * When an address shootdown range exceeds this threshold we invalidate the
> + * entire TLB on the GPU for the given PID rather than each specific address in
> + * the range.
> + */
> +#define ATSD_THRESHOLD (2*1024*1024)
> +
> +/*
>   * Other types of TCE cache invalidation are not functional in the
>   * hardware.
>   */
> @@ -675,11 +682,19 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
>         struct npu_context *npu_context = mn_to_npu_context(mn);
>         unsigned long address;
>
> -       for (address = start; address < end; address += PAGE_SIZE)
> -               mmio_invalidate(npu_context, 1, address, false);
> +       if (end - start > ATSD_THRESHOLD) {

I'm nitpicking, but (end - start) > ATSD_THRESHOLD is clearer

> +               /*
> +                * Just invalidate the entire PID if the address range is too
> +                * large.
> +                */
> +               mmio_invalidate(npu_context, 0, 0, true);
> +       } else {
> +               for (address = start; address < end; address += PAGE_SIZE)
> +                       mmio_invalidate(npu_context, 1, address, false);
>
> -       /* Do the flush only on the final addess == end */
> -       mmio_invalidate(npu_context, 1, address, true);
> +               /* Do the flush only on the final addess == end */
> +               mmio_invalidate(npu_context, 1, address, true);
> +       }
>  }
>

Acked-by: Balbir Singh <bsingharora@gmail.com>

Re: [PATCH 2/2] powernv/npu: Add a debugfs setting to change ATSD threshold

[Balbir Singh]

On Tue, 17 Apr 2018 19:11:29 +1000
Alistair Popple <alistair@popple.id.au> wrote:

> The threshold at which it becomes more efficient to coalesce a range of
> ATSDs into a single per-PID ATSD is currently not well understood due to a
> lack of real-world work loads. This patch adds a debugfs parameter allowing
> the threshold to be altered at runtime in order to aid future development
> and refinement of the value.
> 
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> ---
>  arch/powerpc/platforms/powernv/npu-dma.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> index dc34662e9df9..a765bf576c14 100644
> --- a/arch/powerpc/platforms/powernv/npu-dma.c
> +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> @@ -17,7 +17,9 @@
>  #include <linux/pci.h>
>  #include <linux/memblock.h>
>  #include <linux/iommu.h>
> +#include <linux/debugfs.h>
>  
> +#include <asm/debugfs.h>
>  #include <asm/tlb.h>
>  #include <asm/powernv.h>
>  #include <asm/reg.h>
> @@ -44,7 +46,8 @@ DEFINE_SPINLOCK(npu_context_lock);
>   * entire TLB on the GPU for the given PID rather than each specific address in
>   * the range.
>   */
> -#define ATSD_THRESHOLD (2*1024*1024)
> +static uint64_t atsd_threshold = 2 * 1024 * 1024;
> +static struct dentry *atsd_threshold_dentry;
>  
>  /*
>   * Other types of TCE cache invalidation are not functional in the
> @@ -682,7 +685,7 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
>  	struct npu_context *npu_context = mn_to_npu_context(mn);
>  	unsigned long address;
>  
> -	if (end - start > ATSD_THRESHOLD) {
> +	if (end - start > atsd_threshold) {
>  		/*
>  		 * Just invalidate the entire PID if the address range is too
>  		 * large.
> @@ -956,6 +959,11 @@ int pnv_npu2_init(struct pnv_phb *phb)
>  	static int npu_index;
>  	uint64_t rc = 0;
>  
> +	if (!atsd_threshold_dentry) {
> +		atsd_threshold_dentry = debugfs_create_x64("atsd_threshold",

Nit-picking can we call this atsd_threshold_in_bytes?

> +				   0600, powerpc_debugfs_root, &atsd_threshold);
> +	}
> +
>  	phb->npu.nmmu_flush =
>  		of_property_read_bool(phb->hose->dn, "ibm,nmmu-flush");
>  	for_each_child_of_node(phb->hose->dn, dn) {

Acked-by: Balbir Singh <bsingharora@gmail.com>

Re: [PATCH 1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[Balbir Singh]

On Tue, Apr 17, 2018 at 7:17 PM, Balbir Singh <bsingharora@gmail.com> wrote:
> On Tue, Apr 17, 2018 at 7:11 PM, Alistair Popple <alistair@popple.id.au> wrote:
>> The NPU has a limited number of address translation shootdown (ATSD)
>> registers and the GPU has limited bandwidth to process ATSDs. This can
>> result in contention of ATSD registers leading to soft lockups on some
>> threads, particularly when invalidating a large address range in
>> pnv_npu2_mn_invalidate_range().
>>
>> At some threshold it becomes more efficient to flush the entire GPU TLB for
>> the given MM context (PID) than individually flushing each address in the
>> range. This patch will result in ranges greater than 2MB being converted
>> from 32+ ATSDs into a single ATSD which will flush the TLB for the given
>> PID on each GPU.
>>
>> Signed-off-by: Alistair Popple <alistair@popple.id.au>
>> +       }
>>  }
>>
>
> Acked-by: Balbir Singh <bsingharora@gmail.com>
Tested-by: Balbir Singh <bsingharora@gmail.com>

Re: [PATCH 1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[Alistair Popple]

Sorry, forgot to include:

Fixes: 1ab66d1fbada ("powerpc/powernv: Introduce address translation services for Nvlink2")

Thanks

On Tuesday, 17 April 2018 7:11:28 PM AEST Alistair Popple wrote:
> The NPU has a limited number of address translation shootdown (ATSD)
> registers and the GPU has limited bandwidth to process ATSDs. This can
> result in contention of ATSD registers leading to soft lockups on some
> threads, particularly when invalidating a large address range in
> pnv_npu2_mn_invalidate_range().
> 
> At some threshold it becomes more efficient to flush the entire GPU TLB for
> the given MM context (PID) than individually flushing each address in the
> range. This patch will result in ranges greater than 2MB being converted
> from 32+ ATSDs into a single ATSD which will flush the TLB for the given
> PID on each GPU.
> 
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> ---
>  arch/powerpc/platforms/powernv/npu-dma.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> index 94801d8e7894..dc34662e9df9 100644
> --- a/arch/powerpc/platforms/powernv/npu-dma.c
> +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> @@ -40,6 +40,13 @@
>  DEFINE_SPINLOCK(npu_context_lock);
>  
>  /*
> + * When an address shootdown range exceeds this threshold we invalidate the
> + * entire TLB on the GPU for the given PID rather than each specific address in
> + * the range.
> + */
> +#define ATSD_THRESHOLD (2*1024*1024)
> +
> +/*
>   * Other types of TCE cache invalidation are not functional in the
>   * hardware.
>   */
> @@ -675,11 +682,19 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
>  	struct npu_context *npu_context = mn_to_npu_context(mn);
>  	unsigned long address;
>  
> -	for (address = start; address < end; address += PAGE_SIZE)
> -		mmio_invalidate(npu_context, 1, address, false);
> +	if (end - start > ATSD_THRESHOLD) {
> +		/*
> +		 * Just invalidate the entire PID if the address range is too
> +		 * large.
> +		 */
> +		mmio_invalidate(npu_context, 0, 0, true);
> +	} else {
> +		for (address = start; address < end; address += PAGE_SIZE)
> +			mmio_invalidate(npu_context, 1, address, false);
>  
> -	/* Do the flush only on the final addess == end */
> -	mmio_invalidate(npu_context, 1, address, true);
> +		/* Do the flush only on the final addess == end */
> +		mmio_invalidate(npu_context, 1, address, true);
> +	}
>  }
>  
>  static const struct mmu_notifier_ops nv_nmmu_notifier_ops = {
> 

Re: [1/2] powernv/npu: Do a PID GPU TLB flush when invalidating a large address range

[Michael Ellerman]

On Tue, 2018-04-17 at 09:11:28 UTC, Alistair Popple wrote:
> The NPU has a limited number of address translation shootdown (ATSD)
> registers and the GPU has limited bandwidth to process ATSDs. This can
> result in contention of ATSD registers leading to soft lockups on some
> threads, particularly when invalidating a large address range in
> pnv_npu2_mn_invalidate_range().
> 
> At some threshold it becomes more efficient to flush the entire GPU TLB for
> the given MM context (PID) than individually flushing each address in the
> range. This patch will result in ranges greater than 2MB being converted
> from 32+ ATSDs into a single ATSD which will flush the TLB for the given
> PID on each GPU.
> 
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> Acked-by: Balbir Singh <bsingharora@gmail.com>
> Tested-by: Balbir Singh <bsingharora@gmail.com>

Patch 1 applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/d0cf9b561ca97d5245bb9e0c4774b7

cheers

Re: [2/2] powernv/npu: Add a debugfs setting to change ATSD threshold

[Michael Ellerman]

On Tue, 2018-04-17 at 09:11:29 UTC, Alistair Popple wrote:
> The threshold at which it becomes more efficient to coalesce a range of
> ATSDs into a single per-PID ATSD is currently not well understood due to a
> lack of real-world work loads. This patch adds a debugfs parameter allowing
> the threshold to be altered at runtime in order to aid future development
> and refinement of the value.
> 
> Signed-off-by: Alistair Popple <alistair@popple.id.au>
> Acked-by: Balbir Singh <bsingharora@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/99c3ce33a00bc40cb218af770ef00c

cheers