Messages in this thread Patch in this message | | | Subject | [PATCH v2] ACPI/osl: speedup grace period in acpi_os_map_cleanup | From | Konstantin Khlebnikov <> | Date | Sun, 09 Nov 2014 13:53:37 +0400 |
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ACPI maintains cache of ioremap regions to speed up operations and access to them from irq context where ioremap() calls aren't allowed. This code abuses synchronize_rcu() on unmap path for synchronization with fast-path in acpi_os_read/write_memory which uses this cache.
Since v3.10 CPUs are allowed to enter idle state even if they have RCU callbacks queued, see commit c0f4dfd4f90f1667d234d21f15153ea09a2eaa66 ("rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks"). That change caused problems with nvidia proprietary driver which calls acpi_os_map/unmap_generic_address several times during initialization. Each unmap calls synchronize_rcu and adds significant delay. Totally initialization is slowed for a couple of seconds and that is enough to trigger timeout in hardware, gpu decides to "fell off the bus". Widely spread workaround is reducing "rcu_idle_gp_delay" from 4 to 1 jiffy.
This patch replaces synchronize_rcu() with synchronize_rcu_expedited() which is much faster.
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> Reported-and-tested-by: Alexander Monakov <amonakov@gmail.com> Cc: Tom Boshoven <tomboshoven@gmail.com> Link: https://devtalk.nvidia.com/default/topic/567297/linux/linux-3-10-driver-crash/ --- drivers/acpi/osl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c index 9964f70..217713c 100644 --- a/drivers/acpi/osl.c +++ b/drivers/acpi/osl.c @@ -436,7 +436,7 @@ static void acpi_os_drop_map_ref(struct acpi_ioremap *map) static void acpi_os_map_cleanup(struct acpi_ioremap *map) { if (!map->refcount) { - synchronize_rcu(); + synchronize_rcu_expedited(); acpi_unmap(map->phys, map->virt); kfree(map); }
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