linux-kernel - [PATCH v7 09/24] x86/resctrl: Use __set_bit()/__clear

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Message-Id: <20231025180345.28061-10-james.morse@arm.com>
Date:   Wed, 25 Oct 2023 18:03:30 +0000
From:   James Morse <james.morse@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        James Morse <james.morse@....com>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
        dfustini@...libre.com, amitsinght@...vell.com
Subject: [PATCH v7 09/24] 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.

A subsequent patch adds closid_allocated(), which adds more open
coded bitmaps operations. These will eventually need changing to use
the bitops helpers so that a CLOSID bitmap of the correct size can be
allocated dynamically.

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.

Tested-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
Tested-by: Peter Newman <peternewman@...gle.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
Signed-off-by: James Morse <james.morse@....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.
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 9864cb49d58c..f6051a3e7262 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)
@@ -131,7 +131,7 @@ 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;
+	__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