On Mon, 2014-12-15 at 13:03 +0800, Lee, Chun-Yi wrote:
> From: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
This is now upstream in 3.19-rc1; commit
74b51ee152b6d99e61ba329799a039453fb9438f upstream.
> 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.
>
> Lee, Chun-Yi:
> This patch fixed the performance issue on VMWare workstation 10.0.2 with
> the virtual machine that has more than 2 CPU and 4G memory:
>
> Mware workstation 10.0.2
> BIOS DMI: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference
> Platform, BIOS 6.00 07/31/2013
> vCPU = 8
> vMEM = 4G
> mem.hotplug=TRUE
>
> The physical CPUs on host machine: Intel(R) Xeon(R) CPU X5670 @ 2.93GHz *24
>
> I tested this patch with v3.12, v3.17, v3.18-rc4 kernel, it fixed performance
> issue and got speedup when acpi initial.
>
> Link: https://devtalk.nvidia.com/default/topic/567297/linux/linux-3-10-driver-crash/
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
> Reported-and-tested-by: Alexander Monakov <amonakov@xxxxxxxxx>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> Signed-off-by: Lee, Chun-Yi <jlee@xxxxxxxx>
> ---
> 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);
> }
--
Ben Hutchings
Life would be so much easier if we could look at the source code.
Attachment:
signature.asc
Description: This is a digitally signed message part