The resctrl CLOSID allocator uses a single 32bit word to track which
CLOSID are free. The setting and clearing of bits is open coded.

Convert the existing open coded bit manipulations of closid_free_map
to use __set_bit() and friends. These don't need to be atomic as this
list is protected by the mutex.

Signed-off-by: James Morse <james.morse@arm.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
---
Changes since v6:
 * Use the __ inatomic helpers and add lockdep_assert_held() annotations to
   document how this is safe.
 * Fixed a resctrl_closid_is_free()/closid_allocated() rename in the commit
   message.
 * Use RESCTRL_RESERVED_CLOSID to improve readability.

Changes since v7:
 * Removed paragraph explaining why this should be done now due to badword
   'subsequent'.
 * Changed a comment to refer to RESCTRL_RESERVED_CLOSID.
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index dcffd1c4a476..bc6e0f83c847 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
  * - Our choices on how to configure each resource become progressively more
  *   limited as the number of resources grows.
  */
-static int closid_free_map;
+static unsigned long closid_free_map;
 static int closid_free_map_len;
 
 int closids_supported(void)
@@ -130,8 +130,8 @@ static void closid_init(void)
 
 	closid_free_map = BIT_MASK(rdt_min_closid) - 1;
 
-	/* CLOSID 0 is always reserved for the default group */
-	closid_free_map &= ~1;
+	/* RESCTRL_RESERVED_CLOSID is always reserved for the default group */
+	__clear_bit(RESCTRL_RESERVED_CLOSID, &closid_free_map);
 	closid_free_map_len = rdt_min_closid;
 }
 
@@ -139,17 +139,21 @@ static int closid_alloc(void)
 {
 	u32 closid = ffs(closid_free_map);
 
+	lockdep_assert_held(&rdtgroup_mutex);
+
 	if (closid == 0)
 		return -ENOSPC;
 	closid--;
-	closid_free_map &= ~(1 << closid);
+	__clear_bit(closid, &closid_free_map);
 
 	return closid;
 }
 
 void closid_free(int closid)
 {
-	closid_free_map |= 1 << closid;
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	__set_bit(closid, &closid_free_map);
 }
 
 /**
@@ -161,7 +165,9 @@ void closid_free(int closid)
  */
 static bool closid_allocated(unsigned int closid)
 {
-	return (closid_free_map & (1 << closid)) == 0;
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	return !test_bit(closid, &closid_free_map);
 }
 
 /**
-- 
2.39.2

On 13.02.24 19:44, James Morse wrote:
> The resctrl CLOSID allocator uses a single 32bit word to track which
> CLOSID are free. The setting and clearing of bits is open coded.
> 
> Convert the existing open coded bit manipulations of closid_free_map
> to use __set_bit() and friends. These don't need to be atomic as this
> list is protected by the mutex.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-by: Peter Newman <peternewman@google.com>
> Tested-by: Babu Moger <babu.moger@amd.com>
> Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
> Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
> Reviewed-by: Babu Moger <babu.moger@amd.com>
> ---
> Changes since v6:
>   * Use the __ inatomic helpers and add lockdep_assert_held() annotations to
>     document how this is safe.
>   * Fixed a resctrl_closid_is_free()/closid_allocated() rename in the commit
>     message.
>   * Use RESCTRL_RESERVED_CLOSID to improve readability.
> 
> Changes since v7:
>   * Removed paragraph explaining why this should be done now due to badword
>     'subsequent'.
>   * Changed a comment to refer to RESCTRL_RESERVED_CLOSID.
> ---
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 18 ++++++++++++------
>   1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index dcffd1c4a476..bc6e0f83c847 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
>    * - Our choices on how to configure each resource become progressively more
>    *   limited as the number of resources grows.
>    */

That comment talks about "free CLOSIDs in a single integer". Once could 
think about rephrasing that to "free CLOSIDs in a simple bitmap."

> -static int closid_free_map;
> +static unsigned long closid_free_map;
>   static int closid_free_map_len;
>   
>   int closids_supported(void)
> @@ -130,8 +130,8 @@ static void closid_init(void)
>   
>   	closid_free_map = BIT_MASK(rdt_min_closid) - 1;

Now that we use "unsigned long", I was wondering for a second if we 
should use "proper" bitmap functions here like

	bitmap_fill(closid_free_map, rdt_min_closid);

and converting the alloc path (replace ffs() in closid_alloc()):

	closid = find_first_bit(closid_free_map, closid_free_map_len);
	if (closid == closid_free_map_len)
		return -ENOSPC;
	__clear_bit(closid, &closid_free_map);

(would get rid of the closid-- in closid_alloc())

Just a thought, so

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

Hi David,

On 20/02/2024 16:00, David Hildenbrand wrote:
> On 13.02.24 19:44, James Morse wrote:
>> The resctrl CLOSID allocator uses a single 32bit word to track which
>> CLOSID are free. The setting and clearing of bits is open coded.
>>
>> Convert the existing open coded bit manipulations of closid_free_map
>> to use __set_bit() and friends. These don't need to be atomic as this
>> list is protected by the mutex.

>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index dcffd1c4a476..bc6e0f83c847 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
>>    * - Our choices on how to configure each resource become progressively more
>>    *   limited as the number of resources grows.
>>    */
> 
> That comment talks about "free CLOSIDs in a single integer". Once could think about
> rephrasing that to "free CLOSIDs in a simple bitmap."
> 
>> -static int closid_free_map;
>> +static unsigned long closid_free_map;
>>   static int closid_free_map_len;
>>     int closids_supported(void)
>> @@ -130,8 +130,8 @@ static void closid_init(void)
>>         closid_free_map = BIT_MASK(rdt_min_closid) - 1;
> 
> Now that we use "unsigned long", I was wondering for a second if we should use "proper"
> bitmap functions here like
> 
>     bitmap_fill(closid_free_map, rdt_min_closid);
> 
> and converting the alloc path (replace ffs() in closid_alloc()):
> 
>     closid = find_first_bit(closid_free_map, closid_free_map_len);
>     if (closid == closid_free_map_len)
>         return -ENOSPC;
>     __clear_bit(closid, &closid_free_map);
> 
> (would get rid of the closid-- in closid_alloc())

Yup. I have this as something to post after all the MPAM changes as it's not necessary to
get MPAM going. The patch[0] uses the bitmap APIs you suggest to remove the fixed limit on
the number of CLOSID/PARTID.
MPAM systems are being built with more than 32, but will work without that patch.


> Just a thought, so
> 
> Reviewed-by: David Hildenbrand <david@redhat.com>


Thanks!

James

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/commit/?h=mpam/snapshot/v6.7-rc2&id=b530deed244d9b45f3bce3cccde91f6ed0ebf7ea

On 20.02.24 17:27, James Morse wrote:
> Hi David,
> 
> On 20/02/2024 16:00, David Hildenbrand wrote:
>> On 13.02.24 19:44, James Morse wrote:
>>> The resctrl CLOSID allocator uses a single 32bit word to track which
>>> CLOSID are free. The setting and clearing of bits is open coded.
>>>
>>> Convert the existing open coded bit manipulations of closid_free_map
>>> to use __set_bit() and friends. These don't need to be atomic as this
>>> list is protected by the mutex.
> 
>>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> index dcffd1c4a476..bc6e0f83c847 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>> @@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
>>>     * - Our choices on how to configure each resource become progressively more
>>>     *   limited as the number of resources grows.
>>>     */
>>
>> That comment talks about "free CLOSIDs in a single integer". Once could think about
>> rephrasing that to "free CLOSIDs in a simple bitmap."
>>
>>> -static int closid_free_map;
>>> +static unsigned long closid_free_map;
>>>    static int closid_free_map_len;
>>>      int closids_supported(void)
>>> @@ -130,8 +130,8 @@ static void closid_init(void)
>>>          closid_free_map = BIT_MASK(rdt_min_closid) - 1;
>>
>> Now that we use "unsigned long", I was wondering for a second if we should use "proper"
>> bitmap functions here like
>>
>>      bitmap_fill(closid_free_map, rdt_min_closid);
>>
>> and converting the alloc path (replace ffs() in closid_alloc()):
>>
>>      closid = find_first_bit(closid_free_map, closid_free_map_len);
>>      if (closid == closid_free_map_len)
>>          return -ENOSPC;
>>      __clear_bit(closid, &closid_free_map);
>>
>> (would get rid of the closid-- in closid_alloc())
> 
> Yup. I have this as something to post after all the MPAM changes as it's not necessary to
> get MPAM going. The patch[0] uses the bitmap APIs you suggest to remove the fixed limit on
> the number of CLOSID/PARTID.
> MPAM systems are being built with more than 32, but will work without that patch.

Make sense, thanks!

-- 
Cheers,

David / dhildenb

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     5d920b6881f2249be3a028ce0a7f31c5cc61b1ee
Gitweb:        https://git.kernel.org/tip/5d920b6881f2249be3a028ce0a7f31c5cc61b1ee
Author:        James Morse <james.morse@arm.com>
AuthorDate:    Tue, 13 Feb 2024 18:44:23 
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Fri, 16 Feb 2024 19:18:31 +01:00

x86/resctrl: Use __set_bit()/__clear_bit() instead of open coding

The resctrl CLOSID allocator uses a single 32bit word to track which
CLOSID are free. The setting and clearing of bits is open coded.

Convert the existing open coded bit manipulations of closid_free_map
to use __set_bit() and friends. These don't need to be atomic as this
list is protected by the mutex.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Link: https://lore.kernel.org/r/20240213184438.16675-10-james.morse@arm.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index dcffd1c..bc6e0f8 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -111,7 +111,7 @@ void rdt_staged_configs_clear(void)
  * - Our choices on how to configure each resource become progressively more
  *   limited as the number of resources grows.
  */
-static int closid_free_map;
+static unsigned long closid_free_map;
 static int closid_free_map_len;
 
 int closids_supported(void)
@@ -130,8 +130,8 @@ static void closid_init(void)
 
 	closid_free_map = BIT_MASK(rdt_min_closid) - 1;
 
-	/* CLOSID 0 is always reserved for the default group */
-	closid_free_map &= ~1;
+	/* RESCTRL_RESERVED_CLOSID is always reserved for the default group */
+	__clear_bit(RESCTRL_RESERVED_CLOSID, &closid_free_map);
 	closid_free_map_len = rdt_min_closid;
 }
 
@@ -139,17 +139,21 @@ static int closid_alloc(void)
 {
 	u32 closid = ffs(closid_free_map);
 
+	lockdep_assert_held(&rdtgroup_mutex);
+
 	if (closid == 0)
 		return -ENOSPC;
 	closid--;
-	closid_free_map &= ~(1 << closid);
+	__clear_bit(closid, &closid_free_map);
 
 	return closid;
 }
 
 void closid_free(int closid)
 {
-	closid_free_map |= 1 << closid;
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	__set_bit(closid, &closid_free_map);
 }
 
 /**
@@ -161,7 +165,9 @@ void closid_free(int closid)
  */
 static bool closid_allocated(unsigned int closid)
 {
-	return (closid_free_map & (1 << closid)) == 0;
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	return !test_bit(closid, &closid_free_map);
 }
 
 /**