[PATCH v2 0/5] sched, net: NUMA-aware CPU spreading interface

[PATCH v2 0/5] sched, net: NUMA-aware CPU spreading interface

[Valentin Schneider]

Hi folks,

Tariq pointed out in [1] that drivers allocating IRQ vectors would benefit
from having smarter NUMA-awareness (cpumask_local_spread() doesn't quite cut
it).

The proposed interface involved an array of CPUs and a temporary cpumask, and
being my difficult self what I'm proposing here is an interface that doesn't
require any temporary storage other than some stack variables (at the cost of
one wild macro).

Patch 5/5 is just there to showcase how the thing would be used. If this doesn't
get hated on, I'll let Tariq pick this up and push it with his networking driver
changes (with actual changelogs).

[1]: https://lore.kernel.org/all/20220728191203.4055-1-tariqt@nvidia.com/

Revisions
=========

v1 -> v2
++++++++

o Split _find_next_bit() @invert into @invert1 and @invert2 (Yury)
o Rebase onto v6.0-rc1

Cheers,
Valentin

Valentin Schneider (5):
  bitops: Introduce find_next_andnot_bit()
  cpumask: Introduce for_each_cpu_andnot()
  sched/topology: Introduce sched_numa_hop_mask()
  sched/topology: Introduce for_each_numa_hop_cpu()
  SHOWCASE: net/mlx5e: Leverage for_each_numa_hop_cpu()

 drivers/net/ethernet/mellanox/mlx5/core/eq.c | 12 ++++-
 include/linux/cpumask.h                      | 38 ++++++++++++++++
 include/linux/find.h                         | 44 ++++++++++++++++---
 include/linux/topology.h                     | 46 ++++++++++++++++++++
 kernel/sched/topology.c                      | 28 ++++++++++++
 lib/find_bit.c                               | 23 +++++-----
 6 files changed, 172 insertions(+), 19 deletions(-)

--
2.31.1

[PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Valentin Schneider]

In preparation of introducing for_each_cpu_andnot(), add a variant of
find_next_bit() that negate the bits in @addr2 when ANDing them with the
bits in @addr1.

Note that the _find_next_bit() @invert argument now gets split into two:
@invert1 for words in @addr1, @invert2 for words in @addr2. The only
current users of _find_next_bit() with @invert set are:
  o find_next_zero_bit()
  o find_next_zero_bit_le()
and neither of these pass an @addr2, so the conversion is straightforward.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 include/linux/find.h | 44 ++++++++++++++++++++++++++++++++++++++------
 lib/find_bit.c       | 23 ++++++++++++-----------
 2 files changed, 50 insertions(+), 17 deletions(-)

diff --git a/include/linux/find.h b/include/linux/find.h
index 424ef67d4a42..920597de4e62 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -10,7 +10,8 @@
 
 extern unsigned long _find_next_bit(const unsigned long *addr1,
 		const unsigned long *addr2, unsigned long nbits,
-		unsigned long start, unsigned long invert, unsigned long le);
+		unsigned long start, unsigned long invert1, unsigned long invert2,
+		unsigned long le);
 extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
 extern unsigned long _find_first_and_bit(const unsigned long *addr1,
 					 const unsigned long *addr2, unsigned long size);
@@ -41,7 +42,7 @@ unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, 0UL, 0);
+	return _find_next_bit(addr, NULL, size, offset, 0UL, 0UL, 0);
 }
 #endif
 
@@ -71,7 +72,38 @@ unsigned long find_next_and_bit(const unsigned long *addr1,
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr1, addr2, size, offset, 0UL, 0);
+	return _find_next_bit(addr1, addr2, size, offset, 0UL, 0UL, 0);
+}
+#endif
+
+#ifndef find_next_andnot_bit
+/**
+ * find_next_andnot_bit - find the next set bit in one memory region
+ *                        but not in the other
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+static inline
+unsigned long find_next_andnot_bit(const unsigned long *addr1,
+		const unsigned long *addr2, unsigned long size,
+		unsigned long offset)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr1 & ~*addr2 & GENMASK(size - 1, offset);
+		return val ? __ffs(val) : size;
+	}
+
+	return _find_next_bit(addr1, addr2, size, offset, 0UL, ~0UL, 0);
 }
 #endif
 
@@ -99,7 +131,7 @@ unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
 		return val == ~0UL ? size : ffz(val);
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0);
+	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0UL, 0);
 }
 #endif
 
@@ -247,7 +279,7 @@ unsigned long find_next_zero_bit_le(const void *addr, unsigned
 		return val == ~0UL ? size : ffz(val);
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, ~0UL, 1);
+	return _find_next_bit(addr, NULL, size, offset, ~0UL, 0UL, 1);
 }
 #endif
 
@@ -266,7 +298,7 @@ unsigned long find_next_bit_le(const void *addr, unsigned
 		return val ? __ffs(val) : size;
 	}
 
-	return _find_next_bit(addr, NULL, size, offset, 0UL, 1);
+	return _find_next_bit(addr, NULL, size, offset, 0UL, 0UL, 1);
 }
 #endif
 
diff --git a/lib/find_bit.c b/lib/find_bit.c
index 1b8e4b2a9cba..c46b66d7d2b4 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -21,27 +21,29 @@
 
 #if !defined(find_next_bit) || !defined(find_next_zero_bit) ||			\
 	!defined(find_next_bit_le) || !defined(find_next_zero_bit_le) ||	\
-	!defined(find_next_and_bit)
+	!defined(find_next_and_bit) || !defined(find_next_andnot_bit)
 /*
  * This is a common helper function for find_next_bit, find_next_zero_bit, and
  * find_next_and_bit. The differences are:
- *  - The "invert" argument, which is XORed with each fetched word before
- *    searching it for one bits.
  *  - The optional "addr2", which is anded with "addr1" if present.
+ *  - The "invert" arguments, which are XORed with each fetched word (invert1
+ *    for words in addr1, invert2 for those in addr2) before searching it for
+ *    one bits.
  */
 unsigned long _find_next_bit(const unsigned long *addr1,
-		const unsigned long *addr2, unsigned long nbits,
-		unsigned long start, unsigned long invert, unsigned long le)
+			     const unsigned long *addr2,
+			     unsigned long nbits, unsigned long start,
+			     unsigned long invert1, unsigned long invert2,
+			     unsigned long le)
 {
 	unsigned long tmp, mask;
 
 	if (unlikely(start >= nbits))
 		return nbits;
 
-	tmp = addr1[start / BITS_PER_LONG];
+	tmp = addr1[start / BITS_PER_LONG] ^ invert1;
 	if (addr2)
-		tmp &= addr2[start / BITS_PER_LONG];
-	tmp ^= invert;
+		tmp &= addr2[start / BITS_PER_LONG] ^ invert2;
 
 	/* Handle 1st word. */
 	mask = BITMAP_FIRST_WORD_MASK(start);
@@ -57,10 +59,9 @@ unsigned long _find_next_bit(const unsigned long *addr1,
 		if (start >= nbits)
 			return nbits;
 
-		tmp = addr1[start / BITS_PER_LONG];
+		tmp = addr1[start / BITS_PER_LONG] ^ invert1;
 		if (addr2)
-			tmp &= addr2[start / BITS_PER_LONG];
-		tmp ^= invert;
+			tmp &= addr2[start / BITS_PER_LONG] ^ invert2;
 	}
 
 	if (le)
-- 
2.31.1

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Steven Rostedt]

On Wed, 17 Aug 2022 18:58:08 +0100
Valentin Schneider <vschneid@redhat.com> wrote:

> +#ifndef find_next_andnot_bit
> +/**
> + * find_next_andnot_bit - find the next set bit in one memory region
> + *                        but not in the other
> + * @addr1: The first address to base the search on
> + * @addr2: The second address to base the search on
> + * @size: The bitmap size in bits
> + * @offset: The bitnumber to start searching at
> + *
> + * Returns the bit number for the next set bit
> + * If no bits are set, returns @size.

Can we make the above documentation more descriptive. Because I read this
three times, and I still have no idea what it does.

The tag line sounds like the nursery song "One of these things is not like
the others".

-- Steve


> + */
> +static inline
> +unsigned long find_next_andnot_bit(const unsigned long *addr1,
> +		const unsigned long *addr2, unsigned long size,
> +		unsigned long offset)
> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val;
> +
> +		if (unlikely(offset >= size))
> +			return size;
> +
> +		val = *addr1 & ~*addr2 & GENMASK(size - 1, offset);
> +		return val ? __ffs(val) : size;
> +	}
> +
> +	return _find_next_bit(addr1, addr2, size, offset, 0UL, ~0UL, 0);
>  }
>  #endif

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Valentin Schneider]

On 18/08/22 10:08, Steven Rostedt wrote:
> On Wed, 17 Aug 2022 18:58:08 +0100
> Valentin Schneider <vschneid@redhat.com> wrote:
>
>> +#ifndef find_next_andnot_bit
>> +/**
>> + * find_next_andnot_bit - find the next set bit in one memory region
>> + *                        but not in the other
>> + * @addr1: The first address to base the search on
>> + * @addr2: The second address to base the search on
>> + * @size: The bitmap size in bits
>> + * @offset: The bitnumber to start searching at
>> + *
>> + * Returns the bit number for the next set bit
>> + * If no bits are set, returns @size.
>
> Can we make the above documentation more descriptive. Because I read this
> three times, and I still have no idea what it does.
>
> The tag line sounds like the nursery song "One of these things is not like
> the others".
>

How about:

  find the next set bit in ((first region) AND NOT(second region))

Or

  find the next set bit in (*addr1 & ~*addr2)

?

> -- Steve

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Steven Rostedt]

On Thu, 18 Aug 2022 17:26:43 +0100
Valentin Schneider <vschneid@redhat.com> wrote:

> How about:

> 
>   find the next set bit in (*addr1 & ~*addr2)

I understand the above better. But to convert that into English, we could
say:


  Find the next bit in *addr1 excluding all the bits in *addr2.

or

  Find the next bit in *addr1 that is not set in *addr2.

-- Steve

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Andy Shevchenko]

On Thu, Aug 18, 2022 at 8:18 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> On Thu, 18 Aug 2022 17:26:43 +0100
> Valentin Schneider <vschneid@redhat.com> wrote:
>
> > How about:
>
> >
> >   find the next set bit in (*addr1 & ~*addr2)
>
> I understand the above better. But to convert that into English, we could
> say:
>
>
>   Find the next bit in *addr1 excluding all the bits in *addr2.
>
> or
>
>   Find the next bit in *addr1 that is not set in *addr2.

With this explanation I'm wondering how different this is to
bitmap_bitremap(), with adjusting to using an inverted mask. If they
have something in common, perhaps make them in the same namespace with
similar naming convention?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Valentin Schneider]

On 18/08/22 22:04, Andy Shevchenko wrote:
> On Thu, Aug 18, 2022 at 8:18 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>> On Thu, 18 Aug 2022 17:26:43 +0100
>> Valentin Schneider <vschneid@redhat.com> wrote:
>>
>> > How about:
>>
>> >
>> >   find the next set bit in (*addr1 & ~*addr2)
>>
>> I understand the above better. But to convert that into English, we could
>> say:
>>
>>
>>   Find the next bit in *addr1 excluding all the bits in *addr2.
>>
>> or
>>
>>   Find the next bit in *addr1 that is not set in *addr2.
>
> With this explanation I'm wondering how different this is to
> bitmap_bitremap(), with adjusting to using an inverted mask. If they
> have something in common, perhaps make them in the same namespace with
> similar naming convention?
>

I'm trying to wrap my head around the whole remap thing, IIUC we could have
something like remap *addr1 to ~*addr2 and stop rather than continue with a
wraparound, but that really feels like shoehorning.

> --
> With Best Regards,
> Andy Shevchenko

Re: [PATCH v2 1/5] bitops: Introduce find_next_andnot_bit()

[Yury Norov]

On Fri, Aug 19, 2022 at 11:34:01AM +0100, Valentin Schneider wrote:
> On 18/08/22 22:04, Andy Shevchenko wrote:
> > On Thu, Aug 18, 2022 at 8:18 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> >> On Thu, 18 Aug 2022 17:26:43 +0100
> >> Valentin Schneider <vschneid@redhat.com> wrote:
> >>
> >> > How about:
> >>
> >> >
> >> >   find the next set bit in (*addr1 & ~*addr2)
> >>
> >> I understand the above better. But to convert that into English, we could
> >> say:
> >>
> >>
> >>   Find the next bit in *addr1 excluding all the bits in *addr2.
> >>
> >> or
> >>
> >>   Find the next bit in *addr1 that is not set in *addr2.
> >
> > With this explanation I'm wondering how different this is to
> > bitmap_bitremap(), with adjusting to using an inverted mask. If they
> > have something in common, perhaps make them in the same namespace with
> > similar naming convention?
> >
> 
> I'm trying to wrap my head around the whole remap thing, IIUC we could have
> something like remap *addr1 to ~*addr2 and stop rather than continue with a
> wraparound, but that really feels like shoehorning.

Old and new maps create a simple forward-looking mapping, like this:
    #0   #4
old: 0111 0 ...
     | \\\|
New: 00 111 ...

So if you pass #0, it's wired to 0; but #1 will skip 1 bit and would be
wired to 2; and so on. There is some puzzling when wraparound comes in
play, but the general idea is like that.

I think there's nothing common with bitmap_and{,_not}.

Thanks,
Yury

[PATCH v2 2/5] cpumask: Introduce for_each_cpu_andnot()

[Valentin Schneider]

for_each_cpu_and() is very convenient as it saves having to allocate a
temporary cpumask to store the result of cpumask_and(). The same issue
applies to cpumask_andnot() which doesn't actually need temporary storage
for iteration purposes.

Following what has been done for for_each_cpu_and(), introduce
for_each_cpu_andnot().

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 include/linux/cpumask.h | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 0d435d0edbcb..295b137717bb 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -237,6 +237,25 @@ unsigned int cpumask_next_and(int n, const struct cpumask *src1p,
 		nr_cpumask_bits, n + 1);
 }
 
+/**
+ * cpumask_next_andnot - get the next cpu in *src1p & ~*src2p
+ * @n: the cpu prior to the place to search (ie. return will be > @n)
+ * @src1p: the first cpumask pointer
+ * @src2p: the second cpumask pointer
+ *
+ * Returns >= nr_cpu_ids if no further cpus set in *src1p & ~*src2p
+ */
+static inline
+unsigned int cpumask_next_andnot(int n, const struct cpumask *src1p,
+				 const struct cpumask *src2p)
+{
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
+	return find_next_andnot_bit(cpumask_bits(src1p), cpumask_bits(src2p),
+		nr_cpumask_bits, n + 1);
+}
+
 /**
  * for_each_cpu - iterate over every cpu in a mask
  * @cpu: the (optionally unsigned) integer iterator
@@ -297,6 +316,25 @@ unsigned int __pure cpumask_next_wrap(int n, const struct cpumask *mask, int sta
 		(cpu) = cpumask_next_and((cpu), (mask1), (mask2)),	\
 		(cpu) < nr_cpu_ids;)
 
+/**
+ * for_each_cpu_andnot - iterate over every cpu in one mask but not in the other
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask1: the first cpumask pointer
+ * @mask2: the second cpumask pointer
+ *
+ * This saves a temporary CPU mask in many places.  It is equivalent to:
+ *	struct cpumask tmp;
+ *	cpumask_andnot(&tmp, &mask1, &mask2);
+ *	for_each_cpu(cpu, &tmp)
+ *		...
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_andnot(cpu, mask1, mask2)				\
+	for ((cpu) = -1;						\
+		(cpu) = cpumask_next_andnot((cpu), (mask1), (mask2)),	\
+		(cpu) < nr_cpu_ids;)
+
 /**
  * cpumask_any_but - return a "random" in a cpumask, but not this one.
  * @mask: the cpumask to search
-- 
2.31.1

Re: [PATCH v2 2/5] cpumask: Introduce for_each_cpu_andnot()

[Yury Norov]

On Wed, Aug 17, 2022 at 06:58:09PM +0100, Valentin Schneider wrote:
> for_each_cpu_and() is very convenient as it saves having to allocate a
> temporary cpumask to store the result of cpumask_and(). The same issue
> applies to cpumask_andnot() which doesn't actually need temporary storage
> for iteration purposes.
> 
> Following what has been done for for_each_cpu_and(), introduce
> for_each_cpu_andnot().
> 
> Signed-off-by: Valentin Schneider <vschneid@redhat.com>

I'm concerned that this series doesn't give us real examples and tests
for the new API. If we take it as-is, we'll end up with a dead code for
a while, quite probably for long.

Can you please submit a new code with a real application for the new API?
Alternatively, you can rework some existing code.

Briefly grepping, I found good candidate in a core code: __sched_core_flip(),
and one candidate in arch code: arch/powerpc/kernel/smp.c: update_coregroup_mask.
I believe there are much more.

Regarding the test, I don't think it's strictly necessary to have it as soon as
we'll have real users, but it's always good to backup with tests.

Thanks,
Yury

Re: [PATCH v2 2/5] cpumask: Introduce for_each_cpu_andnot()

[Valentin Schneider]

On 18/08/22 15:38, Yury Norov wrote:
> On Wed, Aug 17, 2022 at 06:58:09PM +0100, Valentin Schneider wrote:
>> for_each_cpu_and() is very convenient as it saves having to allocate a
>> temporary cpumask to store the result of cpumask_and(). The same issue
>> applies to cpumask_andnot() which doesn't actually need temporary storage
>> for iteration purposes.
>>
>> Following what has been done for for_each_cpu_and(), introduce
>> for_each_cpu_andnot().
>>
>> Signed-off-by: Valentin Schneider <vschneid@redhat.com>
>
> I'm concerned that this series doesn't give us real examples and tests
> for the new API. If we take it as-is, we'll end up with a dead code for
> a while, quite probably for long.
>

Tariq has at least two uses of for_each_numa_hop_cpu() (which uses
for_each_cpu_andnot()) in net/mlx5e and net/enic). My plan here is to make
sure the cpumask and sched/topology changes are OK, and then I'd let Tariq
carry the whole set with actual users on top.

I wouldn't want to see this merged without users, especially given the
EXPORT_SYMBOL_GPL() in 3/5.

> Can you please submit a new code with a real application for the new API?
> Alternatively, you can rework some existing code.
>
> Briefly grepping, I found good candidate in a core code: __sched_core_flip(),
> and one candidate in arch code: arch/powerpc/kernel/smp.c: update_coregroup_mask.
> I believe there are much more.
>

Some of these look fairly trivial, I'll have a look around.

> Regarding the test, I don't think it's strictly necessary to have it as soon as
> we'll have real users, but it's always good to backup with tests.
>

That sounds sensible enough, I'll have a look at that.

> Thanks,
> Yury

Re: [PATCH v2 0/5] sched, net: NUMA-aware CPU spreading interface

[Jesse Brandeburg]

On 8/17/2022 10:58 AM, Valentin Schneider wrote:
> Hi folks,
> 
> Tariq pointed out in [1] that drivers allocating IRQ vectors would benefit
> from having smarter NUMA-awareness (cpumask_local_spread() doesn't quite cut
> it).
> 
> The proposed interface involved an array of CPUs and a temporary cpumask, and
> being my difficult self what I'm proposing here is an interface that doesn't
> require any temporary storage other than some stack variables (at the cost of
> one wild macro).
> 
> Patch 5/5 is just there to showcase how the thing would be used. If this doesn't
> get hated on, I'll let Tariq pick this up and push it with his networking driver
> changes (with actual changelogs).

I am interested in this work, but it seems that at least on lore and in 
my inbox, patch 3,4,5 didn't show up.

Re: [PATCH v2 0/5] sched, net: NUMA-aware CPU spreading interface

[Valentin Schneider]

On 18/08/22 09:28, Jesse Brandeburg wrote:
> On 8/17/2022 10:58 AM, Valentin Schneider wrote:
>> Hi folks,
>>
>> Tariq pointed out in [1] that drivers allocating IRQ vectors would benefit
>> from having smarter NUMA-awareness (cpumask_local_spread() doesn't quite cut
>> it).
>>
>> The proposed interface involved an array of CPUs and a temporary cpumask, and
>> being my difficult self what I'm proposing here is an interface that doesn't
>> require any temporary storage other than some stack variables (at the cost of
>> one wild macro).
>>
>> Patch 5/5 is just there to showcase how the thing would be used. If this doesn't
>> get hated on, I'll let Tariq pick this up and push it with his networking driver
>> changes (with actual changelogs).
>
> I am interested in this work, but it seems that at least on lore and in
> my inbox, patch 3,4,5 didn't show up.

I used exactly the same git send-email command for this than for v1 (which
shows up in its entirety on lore), but I can't see these either. I'm going
to assume they got lost and will resend them.

Re: [PATCH v2 0/5] sched, net: NUMA-aware CPU spreading interface

[Valentin Schneider]

On 18/08/22 17:43, Valentin Schneider wrote:
> On 18/08/22 09:28, Jesse Brandeburg wrote:
>> On 8/17/2022 10:58 AM, Valentin Schneider wrote:
>>> Hi folks,
>>>
>>> Tariq pointed out in [1] that drivers allocating IRQ vectors would benefit
>>> from having smarter NUMA-awareness (cpumask_local_spread() doesn't quite cut
>>> it).
>>>
>>> The proposed interface involved an array of CPUs and a temporary cpumask, and
>>> being my difficult self what I'm proposing here is an interface that doesn't
>>> require any temporary storage other than some stack variables (at the cost of
>>> one wild macro).
>>>
>>> Patch 5/5 is just there to showcase how the thing would be used. If this doesn't
>>> get hated on, I'll let Tariq pick this up and push it with his networking driver
>>> changes (with actual changelogs).
>>
>> I am interested in this work, but it seems that at least on lore and in
>> my inbox, patch 3,4,5 didn't show up.
>
> I used exactly the same git send-email command for this than for v1 (which
> shows up in its entirety on lore), but I can't see these either. I'm going
> to assume they got lost and will resend them.

Welp, it's there now, but clearly should've used --no-thread when resending
them :/

[PATCH v2 3/5] sched/topology: Introduce sched_numa_hop_mask()

[Valentin Schneider]

Tariq has pointed out that drivers allocating IRQ vectors would benefit
from having smarter NUMA-awareness - cpumask_local_spread() only knows
about the local node and everything outside is in the same bucket.

sched_domains_numa_masks is pretty much what we want to hand out (a cpumask
of CPUs reachable within a given distance budget), introduce
sched_numa_hop_mask() to export those cpumasks.

Link: http://lore.kernel.org/r/20220728191203.4055-1-tariqt@nvidia.com
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 include/linux/topology.h |  9 +++++++++
 kernel/sched/topology.c  | 28 ++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index 4564faafd0e1..13b82b83e547 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -245,5 +245,14 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
 	return cpumask_of_node(cpu_to_node(cpu));
 }
 
+#ifdef CONFIG_NUMA
+extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
+#else
+static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+#endif	/* CONFIG_NUMA */
+
 
 #endif /* _LINUX_TOPOLOGY_H */
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8739c2a5a54e..f0236a0ae65c 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2067,6 +2067,34 @@ int sched_numa_find_closest(const struct cpumask *cpus, int cpu)
 	return found;
 }
 
+/**
+ * sched_numa_hop_mask() - Get the cpumask of CPUs at most @hops hops away.
+ * @node: The node to count hops from.
+ * @hops: Include CPUs up to that many hops away. 0 means local node.
+ *
+ * Requires rcu_lock to be held. Returned cpumask is only valid within that
+ * read-side section, copy it if required beyond that.
+ *
+ * Note that not all hops are equal in size; see sched_init_numa() for how
+ * distances and masks are handled.
+ *
+ * Also note that this is a reflection of sched_domains_numa_masks, which may change
+ * during the lifetime of the system (offline nodes are taken out of the masks).
+ */
+const struct cpumask *sched_numa_hop_mask(int node, int hops)
+{
+	struct cpumask ***masks = rcu_dereference(sched_domains_numa_masks);
+
+	if (node >= nr_node_ids || hops >= sched_domains_numa_levels)
+		return ERR_PTR(-EINVAL);
+
+	if (!masks)
+		return NULL;
+
+	return masks[hops][node];
+}
+EXPORT_SYMBOL_GPL(sched_numa_hop_mask);
+
 #endif /* CONFIG_NUMA */
 
 static int __sdt_alloc(const struct cpumask *cpu_map)
-- 
2.31.1

[PATCH v2 4/5] sched/topology: Introduce for_each_numa_hop_cpu()

[Valentin Schneider]

The recently introduced sched_numa_hop_mask() exposes cpumasks of CPUs
reachable within a given distance budget, but this means each successive
cpumask is a superset of the previous one.

Code wanting to allocate one item per CPU (e.g. IRQs) at increasing
distances would thus need to allocate a temporary cpumask to note which
CPUs have already been visited. This can be prevented by leveraging
for_each_cpu_andnot() - package all that logic into one ugl^D fancy macro.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 include/linux/topology.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index 13b82b83e547..6c671dc3252c 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -254,5 +254,42 @@ static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
 }
 #endif	/* CONFIG_NUMA */
 
+/**
+ * for_each_numa_hop_cpu - iterate over CPUs by increasing NUMA distance,
+ *                         starting from a given node.
+ * @cpu: the iteration variable.
+ * @node: the NUMA node to start the search from.
+ *
+ * Requires rcu_lock to be held.
+ * Careful: this is a double loop, 'break' won't work as expected.
+ *
+ *
+ * Implementation notes:
+ *
+ * Providing it is valid, the mask returned by
+ *  sched_numa_hop_mask(node, hops+1)
+ * is a superset of the one returned by
+ *   sched_numa_hop_mask(node, hops)
+ * which may not be that useful for drivers that try to spread things out and
+ * want to visit a CPU not more than once.
+ *
+ * To accommodate for that, we use for_each_cpu_andnot() to iterate over the cpus
+ * of sched_numa_hop_mask(node, hops+1) with the CPUs of
+ * sched_numa_hop_mask(node, hops) removed, IOW we only iterate over CPUs
+ * a given distance away (rather than *up to* a given distance).
+ *
+ * hops=0 forces us to play silly games: we pass cpu_none_mask to
+ * for_each_cpu_andnot(), which turns it into for_each_cpu().
+ */
+#define for_each_numa_hop_cpu(cpu, node)				       \
+	for (struct { const struct cpumask *curr, *prev; int hops; } __v =     \
+		     { sched_numa_hop_mask(node, 0), NULL, 0 };		       \
+	     !IS_ERR_OR_NULL(__v.curr);					       \
+	     __v.hops++,                                                       \
+	     __v.prev = __v.curr,					       \
+	     __v.curr = sched_numa_hop_mask(node, __v.hops))                   \
+		for_each_cpu_andnot(cpu,				       \
+				    __v.curr,				       \
+				    __v.hops ? __v.prev : cpu_none_mask)
 
 #endif /* _LINUX_TOPOLOGY_H */
-- 
2.31.1

[PATCH v2 5/5] SHOWCASE: net/mlx5e: Leverage for_each_numa_hop_cpu()

[Valentin Schneider]

Not-signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/eq.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
index 229728c80233..0a5432903edd 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
@@ -812,6 +812,7 @@ static int comp_irqs_request(struct mlx5_core_dev *dev)
 	int ncomp_eqs = table->num_comp_eqs;
 	u16 *cpus;
 	int ret;
+	int cpu;
 	int i;
 
 	ncomp_eqs = table->num_comp_eqs;
@@ -830,8 +831,15 @@ static int comp_irqs_request(struct mlx5_core_dev *dev)
 		ret = -ENOMEM;
 		goto free_irqs;
 	}
-	for (i = 0; i < ncomp_eqs; i++)
-		cpus[i] = cpumask_local_spread(i, dev->priv.numa_node);
+
+	rcu_read_lock();
+	for_each_numa_hop_cpus(cpu, dev->priv.numa_node) {
+		cpus[i] = cpu;
+		if (++i == ncomp_eqs)
+			goto spread_done;
+	}
+spread_done:
+	rcu_read_unlock();
 	ret = mlx5_irqs_request_vectors(dev, cpus, ncomp_eqs, table->comp_irqs);
 	kfree(cpus);
 	if (ret < 0)
-- 
2.31.1