Re: [PATCH] ACPI: Drop rcu usage for MMIO mappings
From: Rafael J. Wysocki
Date: Thu May 07 2020 - 12:43:11 EST
On 5/7/2020 1:39 AM, Dan Williams wrote:
Recently a performance problem was reported for a process invoking a
non-trival ASL program. The method call in this case ends up
repetitively triggering a call path like:
acpi_ex_store
acpi_ex_store_object_to_node
acpi_ex_write_data_to_field
acpi_ex_insert_into_field
acpi_ex_write_with_update_rule
acpi_ex_field_datum_io
acpi_ex_access_region
acpi_ev_address_space_dispatch
acpi_ex_system_memory_space_handler
acpi_os_map_cleanup.part.14
_synchronize_rcu_expedited.constprop.89
schedule
The end result of frequent synchronize_rcu_expedited() invocation is
tiny sub-millisecond spurts of execution where the scheduler freely
migrates this apparently sleepy task. The overhead of frequent scheduler
invocation multiplies the execution time by a factor of 2-3X.
For example, performance improves from 16 minutes to 7 minutes for a
firmware update procedure across 24 devices.
Perhaps the rcu usage was intended to allow for not taking a sleeping
lock in the acpi_os_{read,write}_memory() path which ostensibly could be
called from an APEI NMI error interrupt? Neither rcu_read_lock() nor
ioremap() are interrupt safe, so add a WARN_ONCE() to validate that rcu
was not serving as a mechanism to avoid direct calls to ioremap(). Even
the original implementation had a spin_lock_irqsave(), but that is not
NMI safe.
APEI itself already has some concept of avoiding ioremap() from
interrupt context (see erst_exec_move_data()), if the new warning
triggers it means that APEI either needs more instrumentation like that
to pre-emptively fail, or more infrastructure to arrange for pre-mapping
the resources it needs in NMI context.
Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: 620242ae8c3d ("ACPI: Maintain a list of ACPI memory mapped I/O remappings")
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Erik Kaneda <erik.kaneda@xxxxxxxxx>
Cc: Myron Stowe <myron.stowe@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
linux-acpi is kind of relevant for this too, so please CC it.
---
drivers/acpi/osl.c | 117 +++++++++++++++++++++++++---------------------------
1 file changed, 57 insertions(+), 60 deletions(-)
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 762c5d50b8fe..207528c71e9c 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -214,13 +214,13 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
return pa;
}
-/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
static struct acpi_ioremap *
acpi_map_lookup(acpi_physical_address phys, acpi_size size)
{
struct acpi_ioremap *map;
- list_for_each_entry_rcu(map, &acpi_ioremaps, list, acpi_ioremap_lock_held())
+ lockdep_assert_held(&acpi_ioremap_lock);
+ list_for_each_entry(map, &acpi_ioremaps, list)
if (map->phys <= phys &&
phys + size <= map->phys + map->size)
return map;
@@ -228,7 +228,6 @@ acpi_map_lookup(acpi_physical_address phys, acpi_size size)
return NULL;
}
-/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
static void __iomem *
acpi_map_vaddr_lookup(acpi_physical_address phys, unsigned int size)
{
@@ -263,7 +262,8 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
{
struct acpi_ioremap *map;
- list_for_each_entry_rcu(map, &acpi_ioremaps, list, acpi_ioremap_lock_held())
+ lockdep_assert_held(&acpi_ioremap_lock);
+ list_for_each_entry(map, &acpi_ioremaps, list)
if (map->virt <= virt &&
virt + size <= map->virt + map->size)
return map;
@@ -360,7 +360,7 @@ void __iomem __ref
map->size = pg_sz;
map->refcount = 1;
- list_add_tail_rcu(&map->list, &acpi_ioremaps);
+ list_add_tail(&map->list, &acpi_ioremaps);
out:
mutex_unlock(&acpi_ioremap_lock);
@@ -374,20 +374,13 @@ void *__ref acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
}
EXPORT_SYMBOL_GPL(acpi_os_map_memory);
-/* Must be called with mutex_lock(&acpi_ioremap_lock) */
-static unsigned long acpi_os_drop_map_ref(struct acpi_ioremap *map)
-{
- unsigned long refcount = --map->refcount;
-
- if (!refcount)
- list_del_rcu(&map->list);
- return refcount;
-}
-
-static void acpi_os_map_cleanup(struct acpi_ioremap *map)
+static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
{
- synchronize_rcu_expedited();
+ lockdep_assert_held(&acpi_ioremap_lock);
+ if (--map->refcount > 0)
+ return;
acpi_unmap(map->phys, map->virt);
+ list_del(&map->list);
kfree(map);
}
@@ -408,7 +401,6 @@ static void acpi_os_map_cleanup(struct acpi_ioremap *map)
void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
{
struct acpi_ioremap *map;
- unsigned long refcount;
if (!acpi_permanent_mmap) {
__acpi_unmap_table(virt, size);
@@ -422,11 +414,8 @@ void __ref acpi_os_unmap_iomem(void __iomem *virt, acpi_size size)
WARN(true, PREFIX "%s: bad address %p\n", __func__, virt);
return;
}
- refcount = acpi_os_drop_map_ref(map);
+ acpi_os_drop_map_ref(map);
mutex_unlock(&acpi_ioremap_lock);
-
- if (!refcount)
- acpi_os_map_cleanup(map);
}
EXPORT_SYMBOL_GPL(acpi_os_unmap_iomem);
@@ -461,7 +450,6 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
{
u64 addr;
struct acpi_ioremap *map;
- unsigned long refcount;
if (gas->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY)
return;
@@ -477,11 +465,8 @@ void acpi_os_unmap_generic_address(struct acpi_generic_address *gas)
mutex_unlock(&acpi_ioremap_lock);
return;
}
- refcount = acpi_os_drop_map_ref(map);
+ acpi_os_drop_map_ref(map);
mutex_unlock(&acpi_ioremap_lock);
-
- if (!refcount)
- acpi_os_map_cleanup(map);
}
EXPORT_SYMBOL(acpi_os_unmap_generic_address);
@@ -700,55 +685,71 @@ int acpi_os_read_iomem(void __iomem *virt_addr, u64 *value, u32 width)
return 0;
}
+static void __iomem *acpi_os_rw_map(acpi_physical_address phys_addr,
+ unsigned int size, bool *did_fallback)
+{
+ void __iomem *virt_addr = NULL;
+
+ if (WARN_ONCE(in_interrupt(), "ioremap in interrupt context\n"))
+ return NULL;
+
+ /* Try to use a cached mapping and fallback otherwise */
+ *did_fallback = false;
+ mutex_lock(&acpi_ioremap_lock);
+ virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
+ if (virt_addr)
+ return virt_addr;
+ mutex_unlock(&acpi_ioremap_lock);
+
+ virt_addr = acpi_os_ioremap(phys_addr, size);
+ *did_fallback = true;
+
+ return virt_addr;
+}
+
+static void acpi_os_rw_unmap(void __iomem *virt_addr, bool did_fallback)
+{
+ if (did_fallback) {
+ /* in the fallback case no lock is held */
+ iounmap(virt_addr);
+ return;
+ }
+
+ mutex_unlock(&acpi_ioremap_lock);
+}
+
acpi_status
acpi_os_read_memory(acpi_physical_address phys_addr, u64 *value, u32 width)
{
- void __iomem *virt_addr;
unsigned int size = width / 8;
- bool unmap = false;
+ bool did_fallback = false;
+ void __iomem *virt_addr;
u64 dummy;
int error;
- rcu_read_lock();
- virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
- if (!virt_addr) {
- rcu_read_unlock();
- virt_addr = acpi_os_ioremap(phys_addr, size);
- if (!virt_addr)
- return AE_BAD_ADDRESS;
- unmap = true;
- }
-
+ virt_addr = acpi_os_rw_map(phys_addr, size, &did_fallback);
+ if (!virt_addr)
+ return AE_BAD_ADDRESS;
if (!value)
value = &dummy;
error = acpi_os_read_iomem(virt_addr, value, width);
BUG_ON(error);
- if (unmap)
- iounmap(virt_addr);
- else
- rcu_read_unlock();
-
+ acpi_os_rw_unmap(virt_addr, did_fallback);
return AE_OK;
}
acpi_status
acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
{
- void __iomem *virt_addr;
unsigned int size = width / 8;
- bool unmap = false;
+ bool did_fallback = false;
+ void __iomem *virt_addr;
- rcu_read_lock();
- virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
- if (!virt_addr) {
- rcu_read_unlock();
- virt_addr = acpi_os_ioremap(phys_addr, size);
- if (!virt_addr)
- return AE_BAD_ADDRESS;
- unmap = true;
- }
+ virt_addr = acpi_os_rw_map(phys_addr, size, &did_fallback);
+ if (!virt_addr)
+ return AE_BAD_ADDRESS;
switch (width) {
case 8:
@@ -767,11 +768,7 @@ acpi_os_write_memory(acpi_physical_address phys_addr, u64 value, u32 width)
BUG();
}
- if (unmap)
- iounmap(virt_addr);
- else
- rcu_read_unlock();
-
+ acpi_os_rw_unmap(virt_addr, did_fallback);
return AE_OK;
}