Re: Reading EeePC900 battery info causes stalls

[Alexey Starikovskiy <aystarik@gmail.com>]

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Hi Sitsofe,

I think the least troubling place to add cond_resched() is then ACPICA 
is exiting interpreter.
Please check if the attached patch helps with latencies.

Regards,
Alex.

Sitsofe Wheeler wrote:
> (Long thread that was originally posted over here: 
> http://tinyurl.com/4akxa5 )
>
> I've found that when running on battery (and the battery is not full) 
> the system will stall while battery information is read when using a 
> non preemptive kernel.
>
> I can reliably hear the stalls at runlevel 1 by running
> speaker-test -b75000
> and
> watch --interval=1 cat /proc/acpi/battery/BAT0/info
> within separate terminals within screen.
>
> I have ftraces of the stalls but the traces become large very quickly. 
> To that end I have disabled the tracing of certain functions to allow 
> part of the traces to be produced.
>
> By doing counts across multiple runs I would say that the most 
> frequently called functions are the following (in most frequently 
> called order). The counts are definitely approximate but are 
> reasonable relative to each other.
>
>  475325 acpi_os_release_object (acpi_ut_delete_generic_state)
>  406895 kmem_cache_free (acpi_os_release_object)
>  402838 kmem_cache_alloc (acpi_ut_create_generic_state)
>  132968 acpi_ut_update_ref_count (acpi_ut_update_object_reference)
>  131041 acpi_ut_pop_generic_state (acpi_ut_update_object_reference)
>  131036 acpi_ut_delete_generic_state (acpi_ut_update_object_reference)
>  131025 acpi_ut_create_generic_state (acpi_ut_create_update_state)
>  131023 acpi_ut_create_update_state_and_push 
> (acpi_ut_update_object_reference)
>  131020 acpi_ut_create_update_state 
> (acpi_ut_create_update_state_and_push)
>  131018 acpi_ut_push_generic_state (acpi_ut_create_update_state_and_push)
>   60147 acpi_ns_get_next_node (acpi_ns_delete_namespace_by_owner)
>   28974 acpi_ns_get_next_valid_node (acpi_ns_get_next_node)
>
>
> Here's the command line I used to disable the tracing of certain 
> frequent functions:
>
> echo acpi_os_release_object > set_ftrace_notrace && echo kmem_cache_* 
> >> set_ftrace_notrace && echo acpi_ut_* >> set_ftrace_notrace
>
> Logs with the filtering on can be seen here (15Mbytes decompressed each):
> http://sucs.org/~sits/test/eeepc-debug/20080923/latency_trace.gz
> http://sucs.org/~sits/test/eeepc-debug/20080923/trace.txt.gz
>
> I guess the aim is to find a good point to put cond_resched() or 
> otherwise solve the latency issue.
>


[-- Attachment #2: add_cond_resched_to_ACPI.patch --]
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diff --git a/drivers/acpi/executer/exutils.c b/drivers/acpi/executer/exutils.c
index 86c0388..3c715d0 100644
--- a/drivers/acpi/executer/exutils.c
+++ b/drivers/acpi/executer/exutils.c
@@ -143,6 +143,8 @@ void acpi_ex_reacquire_interpreter(void)
  *
  ******************************************************************************/
 
+#include <linux/sched.h>
+
 void acpi_ex_exit_interpreter(void)
 {
 	acpi_status status;
@@ -154,7 +156,7 @@ void acpi_ex_exit_interpreter(void)
 		ACPI_ERROR((AE_INFO,
 			    "Could not release AML Interpreter mutex"));
 	}
-
+	cond_resched();
 	return_VOID;
 }